Friday, May 18, 2012

The Other Early Tandy 1000s

Some people may have noticed the prior post in which I extoll the virtues of the Tandy 1000SX.  I recently posted on the later Tandy 1000 models, which increasingly stray from the standards established by the PCjr. and original 1000.  But let me examine the issues with the other systems.

Tandy 1000TX - This system is equal to or better than the SX in every way but two.  It is better in that it has an 80286 CPU, is upgradeable to 768K RAM (to allow full 640K conventional), has a volume control dial for the internal speaker, a front-case mounted headphone jack which reroutes the audio from the internal speaker (no multiplexer nonsense), has a serial port, comes with a 720K drive and boots up a lot faster.  However, it provides power through the drive cable, which needs to be accounted for by cutting holes in the pins feeding power to any floppy drive not supporting that arrangement.  This is only slightly annoying.  Even so, the power supply has one 4-pin Molex connector for the 5.25" floppy drive, which can be split with a common Y-adapter.  

The other issue is that the system is by default faster than the SX, even with a 286 Express accelerator.  While it can cut the speed of the CPU by half, even a 286 at half speed is substantially faster than an SX without an accelerator.

I would estimate that, based on benchmarks of both systems, Tandy 1000TX running at 4MHz would be somewhat faster than a Tandy 1000SX with a V20 upgrade running at 7.16MHz. However, this is still about 2x faster than an IBM PC with an 8088 running at 4.77MHz. Already you have three noticeable speed increases over the original PC and the software written when that was the only thing around. So if the lower speeds are important to you, then the TX may not be a good choice.  Despite running its CPU at 8MHz, the TX and TL machines are approximately 10% slower than an IBM AT @ 8MHz, but have faster video than IBM EGA.

The 286 is in a PLCC socket, so most 386 and 486 upgrade devices work in it, if you can find one.  However, it still has 8-bit slots, so you will need to find VGA, IDE, HD Floppy and Network cards that will work in an 8-bit slot.

Tandy 1000EX - This was released at the same time as the SX, and is essentially a stripped down of the SX.  It even uses the same BIOS as the SX, shares the 7.16/4.77MHz speed switch.  Unfortunately, expansion is really difficult in this machine as it has one bay that is supposed to contain a 5.25" floppy drive.  No reset switch either, no way to use a different keyboard, and due to internal RF shielding it is extremely difficult to get inside to the motherboard.  I also read that installing a RTC chip is also difficult due to lack of clearance that the internal shielding imposed.  No coprocessor can be installed without an extremely rare adapter.  The video is difficult to upgrade at best but it is possible despite what Tandy may have told customers.

The worst issue with these machines are the PLUS slots and finding expansion boards.  A PLUS slot is simply a 62-pin ISA with berg-strip pins and connectors mounted at a right angle to a regular card edge ISA connector.  However, the brackets securing the cards to the chassis are a custom design.  Finally, to upgrade the RAM and add DMA you need a special PLUS board similar to the boards for the original 1000s. The most common upgrades to find would be serial cards and modems, and while specialty companies made other upgrade devices, they are extremely difficult to find.  There is a port for an external 5.25" or 3.5" drive, but the pinout is a Tandy proprietary design.  You can switch the boot drive using the F4 key at bootup.  If you have a 3.5" drive, you will need DOS 3.2 and drivparm in your config.sys to obtain the full benefit from it.

The lack of on-board DMA, which users of other computers took for granted, is extremely irritating.  Without DMA, most hard drive options are out of reach.  Standard MFM/RLL controllers use DMA and memory mapped interface cards like the Trantor T-128 SCSI and the Silicon Valley Computer ADP-50L IDE boards require it to enable their improved performance.  You may be able to use a port I/O SCSI interface like the Trantor T-130B, but that will not work reliably unless you have a V20, V30 or 286 CPU.

The other issue is the floppy drive.  Without DMA, the CPU must handle all the transfers to and from the floppy drive.  This requires tight timing and disabling interrupts, so serial (mouse and modem) and keyboard input may be lost during floppy drive access.  DMA makes using old machines much easier.

The machine does have two small benefits over the SX.  First, it has an external volume dial that can control the headphone or internal speaker.  The SX has a potentiometer inside to adjust the volume, but it isn't very practical to open the case.  Second, due to the design you will always get sound output from the jack, unlike the RCA audio output of the 1000 or 1000SX.  On the latter machines you may have to set bits in the audio multiplexer.  No 8087 coprocessor socket.

Tamdy 1000HX - This update to the EX shares most of its benefits and drawbacks, but adds more in both directions.  It was released alongside the TX.  Unlike the EX, it has two internal 3.5" bays, although if you want to use them for anything other than Tandy drives you may need some ingenuity in getting other things to fit in them.  It can support a third external floppy drive, which can be a 5.25" or a 3.5" drive in addition to the two internal drives.

It has better clearance for installing a clock chip and less RF shielding to contend with.  However, it uses power-in-drive cabling for the floppy drives and there are no molex connectors available for powering something else.  Although it only comes with DOS 2.11, Tandy modified that DOS to provide full support for 3.5" floppy drives.  In theory I suppose that could confuse 3.5" DD floppy programs that say "requires DOS 3.2".  It also has DOS-in-ROM, so you don't need a DOS floppy in the drive for simply running applications or have to wait on slow floppy disk accesses to your DOS disk.  The machine boots instantly to a menu allowing you to select to boot to a program in drive A:, start from the C: (ROM) drive, or enter Deskmate.

Tandy 1000/A/HD - This is the original model, and it sort of a trial run for the later machines.  They have three slots and can expand memory through the use of ISA boards.  The original Tandy 1000, (non-A version), has no socket for a numeric 8087 coprocessor.  You can burn and insert EPROMs to upgrade to the 01.01.01 BIOS of the 1000A.

The built in graphics cannot be disabled and and using an EGA or VGA card is tricky at best.  I do not think that the early 1000s supported the use of a monochrome or Hercules card because there would be no BIOS support for it.

There are only 3 ISA slots, and at least one is required to expand the system beyond 128K and add DMA. Tandy originally released two RAM expansion boards, the first with the DMA chip and up to 256K (25-1004) and the second without.the DMA chip and up to 256K (25-1009).  Any RAM card with settable memory addresses like an AST Six Pak Plus (short versions) will work in place of the second card.

For the 1000HD, Tandy included a new board (25-1011) with the DMA chip and allowing you to add up to 512K.  It also has a PLUS header allowing you to use a PLUS card, like the serial card, without having to take up another precious slot.  The 1000HD also comes with a 10MB MFM hard drive (Tandon TM-252) taking up one of the two 5.25" bays and the interface card (WD1002S-WX2).

Like the SX, the Tandy 1000/A/HD can use the 286 Express Accelerator.  The accelerator consists of an ISA card and a daughterboard with a ribbon cable to the motherboard's CPU socket.  The Tandy 1000A and 1000HD share the same motherboard, and can use the came daughtercard that the SX can use.  The original 1000 requires a different daughteboard, and the regular card is hard enough to find as it is.    An NEC V20 will give a modest speed boost.

The Tandy 1000/A/HD system does not assign bootup functions to the F1-F4 keys as the later Tandys do.  Since there is only one speed, there is no function for the fast/slow speed, and swap drives is not available (since only one type of drive was supported during these systems' life).  Neither is the mono mode, and TV mode (40 columns with 200 lines) requires pressing F12 at bootup.  However, the 1000A or the 1000 with upgraded BIOS will allow you to use F1 to enter the mono mode.

There is no volume control and the same issues with the sound multiplexer and the RCA audio out on the SX will be encountered in these machines.  Unlike the SX, there is no switch to use IRQ2 instead of IRQ5 for the video (so you can use an IRQ2 hard drive controller).  The Power Supply is rated for 54W compared with the 65W of the SX and TX.  None of these machines have a Real-Time Clock (RTC), which must be added via a plug-in module.  The Dallas DS-1215 is the usual choice.  

Wednesday, May 16, 2012

Benefits and Drawbacks of the Late Model Tandy 1000s

In 1988, Tandy decided to make its very successful 1000 series more like standard PCs and less quirky like its original models.  The early model Tandy 1000s were the 1000, A, HD, EX, SX, HX, TX.  Late model means Tandy TL, TL/2, TL/3, SL, SL/2, RL, RL-HD, RLX, RLX-HD, RLX-B, RLX-B-HD, RSX, RSX-HD.  Now, the later Tandys had some significant advantages over the earlier machines, but they also have their drawbacks too.  Lets start with the advantages :

Bays : (TL, TL/2, TL/3)

The first models in the series, the Tandy TL and Tandy SL, were intended to replace the TX and SX in the product line.  The TLs have three bays whereas the rest of the Tandys have two.  While you do lose some flexibility compared with the two 5.25" bays of the earlier models and SL, you can use one of the 3.5" bays for an internal hard drive.

Drives : (all except SL)

All late model Tandys come with 3.5" drives, which makes using the machines with modern PCs a lot easier.   The drives use 720K disks, except for the RLX and RSX, but most 1.44MB USB drives can read and write 720K disks.  You can use tape over the hole of HD disks, but best results will be had with true 720K disks.

DOS-in-ROM :

DOS in ROM makes it easier to use the machine without a hard drive.  Essentially, the DOS-in-ROM allows you to use DOS formatted disks without needing to have DOS in a floppy drive.  Makes for much more convenient and speedier basic disk operations.  The DOS in ROM does not include utilities, so you will still need your DOS disks if your programs require DOS utilities.  If you have a hard drive, this functionality is disabled.

Fast Booting :

Although the HX and TX started this trend, all late models boot up virtually instantaneously.  From the time you turn the power switch on or press reset until the computer begins booting your floppy or hard drive, the time the machine takes is negligible.  With DOS-in-ROM, a decent hard drive or compact flash, you will not have to wait for the machine to boot into DOS.

Real Time Clock (TL, TL/2, TL/3, RL-HD, RLX, RLX-B, RLX-B-HD, RSX, RSX-HD) :

The Real Time Clock uses a standard CR2032 Battery in a clip.  It is easy to replace.  Other systems of this time and later use nasty rechargeable barrel-type batteries or hard to find Dallas 1287 RTCs which have the battery inside the plastic casing.  No drivers are required if using Tandy DOS.  If you are using a generic DOS, you may need to find a driver, but there is a Tandy MS-DOS 5.00.  Nothing higher should be needed for these systems.  The SL, SL/2, non-HD RL needs the chip, Dallas DS1216E, installed in a particular socket and has no clip-on battery

EEPROM Saving :

The system settings are stored in a small EEPROM and accessed by a setup program.  Earlier systems (HX excluded), had few options to set and those that did would require special parameters (drivparm in config.sys for 720K drives) or jumpers.

Keyboard :

Standard XT keyboards will work and any that can switch to XT mode.  IBM Model F XT keyboards work perfectly, and IBM Made (1992 or earlier) Model M keyboards work very well after the first keypress.  The Tandy Enhanced Keyboard which came with these systems can work in XT or AT machines, even modern ones.  I don't care for the action on the Tandy keyboard, however.

PS/2 Keyboard & Mouse  (TL/3, RL, RL-HD,  RLX, RLX-HD, RLX-B, RLX-B-HD, RSX, RSX-HD ):

Tandy was particularly forward thinking here, including PS/2 ports for the keyboard and mouse on these systems.  No adapters are necessary, and serial mice are slightly more difficult to find than PS/2 mice.  Tandys except for the RSX/RSX-HD do not have high IRQs available, and the PS/2 mouse usually uses IRQ 12.  The PS/2 mouse of the Tandys uses IRQ3 with the exception noted above, but the cutemouse driver will work fine with the port.  Windows will not.

Disable Joystick Ports :

If you do not want to modify a standard PC joystick to work in a Tandy joystick port, which requires building an adapter and internally connecting the third terminal of your joystick axes to ground, you can disable the Tandy joystick ports and use the ports on a standard PC gameport adapter or sound card.  Although Tandy did not support doing this, it can be done by setting bit 1 at I/O FFEB to 1.

The RLX-B(-HD) has an 8-pin mini-DIN that requires an adapter to use the regular 6-pin DIN Tandy joysticks.

Card Edge Printer Port Disable (TL,TL/2,SL,SL/2) :

This port is a leftover from the TRS-80s and is designed to be compatible with the pre-IBM Centronics standard.  It is not bidirectional and the nybble unidirectional mode doesn't work either.  I am unsure whether it can be disabled in the setup program, but it should be disabled by setting bit 1 of I/O 0065 to 0.  Other late Tandys come with standard DB-25 ports that are or can be made to work in the bidirectional mode (except the RL and RL-HD).

Built-in Floppy Port Disable (TL,TL/2,SL,SL/2, RL, RL-HD):

You can disable the double density only floppy port through the setup program, allowing for conflict free usage of a high density floppy drive.  The TL/3, RLX and RSX come with HD floppy controllers, so even if you could disable them, why would you want to?

Built-in Serial Port Availability and Disable :

All these systems come with a built-in serial port, as does the TX.  I am also unsure whether you can disable the 8250B only serial port through the setup program, but it should be doable by setting bit 4 of I/O 0065 to 0.  This would allow for the use of a 16450/16550 serial UART controller.

Built-in Graphics Disable (TL, TL/2, TL/3, SL, SL/2, RL, RL-HD)  :

The built-in graphics of these Tandys, which are similar to EGA but not compatible with it, can be disabled by plugging in an EGA or VGA card.  A program called VGAFIX.COM is required for proper autodetection by some programs.  Finding a VGA card that can work in an 8-bit slot will require a bit of work, but the earlier the card, the better.  However, even some of the VGA cards using the very fast TSENG ET4000AX cards can work.  I am not sure whether the built-in VGA can be disabled the RLX or the SVGA in the RSX, but I doubt anyone would want to sacrifice a slot for that.

CPU Upgradeability (TL, TL/2, TL/3, SL, SL/2)  :

The TLs have socketed PLCC 80286s into which plug-in 386 and 486 upgrades can be installed.  Unfortunately, due to the lack of extended memory and the difficulty of finding an 8-bit EMS board that will fit in these systems, the functionality is far from a real 386/486.  The SLs can have their DIP 8086s replaced with NEC V30s for a speed boost.

Volume Control, Earphone and Microphone Jacks and Reset Switch :

An adjustable knob on the front of the machine allows the user full control over the volume of the internal speaker.  Also found on the EX, HX & TX.  Reset can be easily accomplished if the system refuses to accept keyboard input, unlike on the EX and HX.  Microphone jacks can be used to record sound, and can usually be set to line in as well.

Full 640K Conventional Memory (TL, TL/2, TL/3, RL, RL-HD, RLX, RLX-B, RLX-B-HD, RSX, RSX-HD) :

Unlike all the earlier Tandys except the TX, most of the later models have a 128K upgrade so that the full 640K is available instead of 32K or more taken by the built-in graphics.  (RLX & RSX do not apply as they have VGA, which does not rob from system RAM)

Expanded/Extended Memory (RLX, RLX-B, RLX-B-HD, RSX, RSX-HD) :

The RLX/RLX-B can be upgraded to 1MB of RAM, and the HD versions have the 1MB preinstalled.  640K is conventional, 384K is extended.  I assume the the 384K of extended is mapped above 1MB, so it can only be used for whatever you can use extended memory.  You can use it to load DOS high and save about 40K using HIMEM.SYS /M:2.  You can also use it for games that support the XMS standard, SMARTDRV disk cache and programs that use the 286's protected mode like Windows 3.0 & 3.1.  Unfortunately, more games used EMS than XMS because EMS works in 808x machines, but EMS is not possible on this machine unless you use its slot for an EMS board.  The RSX can be upgraded to 9MB, and that can be easily configured to act as expanded or extended memory thanks to the 386's memory controller and EMM386.EXE and HIMEM.SYS.

Compact and Silent Running  (RL, RL-HD, RLX, RLX-B, RLX-B-HD, RSX, RSX-HD)

These machines are very small, both in terms of case height/width/depth and the motherboard size.  Additionally, their power supplies are only 25W, so they do not use a fan.  This means that unless you are accessing a drive motor or using the speaker, these machines run silently.  The drawback is the limited expansion, one or two ISA slots only.  The bidirectional parallel port can help out here.

Drawbacks :

Video :

No composite video

None of the later Tandys support composite video output, while all the early ones do.  Although there are detection issues, you can put a CGA card in these Tandys for composite video output.  Unlike the early Tandys and PCjr., you will be limited to the CGA modes for composite color.

Hercules graphics  (TL, TL/2, TL/3, SL, SL/2, RL, RL-HD)

Games autodetecting Tandy may not work with the Hercules emulation found in the Tandy Video II chip.  They detect a Tandy 1000 and assume that the user wants to use Tandy graphics, regardless of any other functionality detected.  Of course, since most games look better with color graphics, the Hercules/MDA functionality is likely to go unused.  Dual monitor support, using a splitter cable, is theoretically possible, however, this may endanger your monitors, which function at different sync rates.  A CGA and a MDA monitor may be damaged if the other's monitor's scan rates are sent to it.

Audio :

Slight audio issues :

There maybe some missing notes in Tandy music.  The first note of Greensleeves on KQ1 (DOS) and KQ2 (booter or DOS) will not play on any later Tandy.  This is because the Sierra AGI engine will send a command to set the audio multiplexer to output to the RCA jacks on the Tandy 1000 and SX.  This functionality is not required for any other Tandy, and the write will reset the PSSJ chip in the later models, causing the first note not to be played.  The early Tandys and PCjr. have a discrete sound chip, the TI SN 76496, but the later Tandys have that functionality built into its PSSJ chip.

The digital audio recording for the TL and SL is speed dependent.  The TL/2 and SL/2 and later Tandy's have a double buffered input, so recording audio is no longer speed dependent.

Conflicts with devices using DMA1

The later Tandys will freeze if a Sound Blaster 1.0-2.0, which cannot use anything else but DMA1, is installed in the system if digitized sound is played back.  You may encounter this in a game supporting either Sound Blaster or the Tandy DAC.  There may also be problems, for example, with a Central Point Software CopyIIPC Option Board, which must use DMA1 in a Tandy 1000 (can share DMA2 in an IBM PC).

No Tandy sound (RLX, RLX-HD, RLX-B, RLX-B-HD, RSX, RSX-HD)

The RLX and RSX really strayed far from the Tandy 1000 standard.  The RLX does  not support Tandy graphics because it has a standard VGA built into the motherboard.  So games that autodetect the graphics and sound may not play the Tandy sounds if they find a non-Tandy graphics adapter in the system.  The RSX went even further from the compatibility ideal, as it had moved the sound chip from I/O C0 to 1E0 because it supported the 2nd DMA controller, which can be found at C0.  Most programs supporting Tandy sound were released prior to the RSX and were unaware of the move.  Moreover, there were no BIOS routines for the music, the programmer had to write to the sound chip directly.  There were BIOS routines for digitized sound playback, so if the game used them, that sound would work.  Not all games did.  The Tandy 2500XL also had the sound chip relocated, so you can use that selection if your game supports it.

No joystick during digital audio playback

The PSSJ chip will not allow joystick reads while it is playing back digitized sounds.  This may only be slightly annoying, as most games of the time period only use short snippets.  However, if the game uses frequent digital samples, then it may disable the joystick entirely.  I doubt it would read from an IBM gameport, since it does not expect one to be in a Tandy 1000.


Keyboard :

Programs demanding the original Tandy 1000 keyboard may have serious difficulties.  First, the scan codes for the F11, F12 and dedicated cursor keys on the original Tandy 1000 keyboard cannot be generated by the corresponding key of a standard 101-key keyboard, whether in XT or AT mode.  This is usually not too much of a problem as most programs in the 1980s did not use F11 & F12 and would allow you to use the numeric keypad as cursor keys.  Any games that rely on differences in the Tandy keyboard may be tricky  or impossible  to play on an IBM PC keyboard.  Finally, some games may refuse to accept input (Snow Strike) or freeze (King's Quest Tandy Booter) on some keys because they expect the Tandy keyboard and get an IBM keyboard instead.

On the SL and TL, it may be possible to make an adapter to allow the original 1000 keyboard to work.

Joystick :

Programs requiring the Tandy joystick port used may not read the stick correctly if the Tandy ports are disabled and an IBM PC joystick is being used instead.  There are differences in how the ports work at the electrical level.  Really early games would not know of the Tandy joystick and their tight timing loops may be thrown off by the differences.  Later games may take those differences into account in their reading routines and not work properly because the hardware does not exactly match what they are expecting.  I do not know of a game that definitively has this issue, so this may be more of a theoretical than a real compatibility issue.

Interfaces :

Power-in-Drive Cables (TL, TL/2, TL/3, SL/2, RL, RL-HD, RLX, RLX-HD, RLX-B, RLX-B-HD, RSX, RSX-HD) :

In a normal IBM PC, power is supplied to drives on a separate cable with a 4-pin Molex or mini-Molex plug from the 34-pin data ribbon cable.  In all Tandys from the TX and HX onward, except for the SL, +5 and +12 v is supplied on what would otherwise be ground pins on a normal drive cable. Some Tandy cables, which tend to be no longer than absolutely necessary for Tandy supplied drives, had holes punched in the cables for a 5.25" drive.

8-bit IDE interface (TL/2, TL/3, RL, RL-HD, RLX, RLX-HD, RLX-B, RLX-B-HD) :

This may have been a good idea at the time, but today is fairly useless.  In the early days of the IDE standard, there was an 8-bit version released for 8-bit machines.  As Tandy never implemented 16-bit slots or 16-bit IDE ports until the RSX on the 1000 series, they sold 8-bit IDE drives.  Unfortunately these drives are very difficult to find today and only come in 20 and 40MB varieties.  Regular 16-bit IDE hard drives and compact flash drives will not work with these ports.  Compared to the TL, the TL/2 and TL/3 sacrifice a slot for this interface.

8-bit slots (TL, TL/2, TL/3, SL, SL/2, RL, RL-HD, RLX, RLX-HD, RLX-B, RLX-B-HD) :

Unfortunately, even though half systems have a 80286 and therefore naturally support 16-bit data bus transfers, Tandy crippled their machines.  Only the RSX has 16-bit slots, and it is the least compatible of the lot.  All the above machines could have supported a full or crippled ISA slot.  The 8086 supports a 16-bit data bus and the upper address lines on a 16-bit slot are not used on all cards.  The same could be said for the TX as well.