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.


  1. I sold my Tandy 1000 TL/2 a month or so ago. Great article on the pros and cons, in the year or so I had my Tandy, I never saw any reason to use it over any other retro system, save for the Tandy sound in early Sierra games.

  2. Regarding "No true 80x25 200 line mode" -- I wonder if the 6845 is set to 9 rows per char in the 225-line modes -- if so, it should be a simple matter to reprogram it to go back to 200 lines. Has anyone ever tried to fix this? I have a Tandy 1000 TX + CM-5 I could hook up to see if a little hacking works.

  3. Fascinating info! There's just one little question I've been wondering about and haven't been able to find the answer to:

    The 8086 CPU in the SL has a 16-bit data bus. Does the PCB in the SL support 16-bit transfers with the RAM, or did Tandy cripple the SL as they did the TX/TL with a clipped 8-bit bus ??

    I expect they did since the SL was the junior member of the 1000 family of that era. But I have not been able to confirm this suspicion.

    Incidentally, I read somewhere else on the web that the SL will only address some 570 kilobytes of RAM, even when upgraded to the physical maximum of 640K. Another reason to suspect a deliberate stunting of the SL.

    Tandy has other historical examples of this practice. When they were still selling their last incarnation of the original Z-80 based TRS-80 (the Model 4D), they could easily have modernized it with 3.5" drives, megabyte RAM, 8 Mhz Z-80H, etc. But Tandy was a corporate behemoth comprised of some half-dozen or more computer lines/departments that were competing against one another as with the rest of the industry. Their various product managers were eager to stunt each other's efforts lest their in-Tandy rivals steal sales from one another. Cf. the General Motors marketing model.

  4. wiki leaker :

    All Tandys with a CPU that uses a 16-bit data bus support a 16-bit data path to the RAM. That includes the TX, TL, TL/2, TL/3, SL, SL/2, RL, RL-HD, RLX, RLX-HD, RLX-B & RLX-B-HD, RSX and RSX-HD. I imagine it would be more expensive to try to cripple the machines with an 8-bit path.

    The issue with the the expansion slots, because except for the RSX, they all use only the 8-bit ISA connector. Any cards that require a 16-bit card, mainly for the data bus, will not work in these systems unless they specifically support 8-bit operation.

    The SL and SL/2 supports 640KB on the motherboard, just like the SX. However, 32KB is generally taken for video, and DOS loads the OS after that. The end result could very well be 570KB free. However, most Tandy games only require 512KB free. Some systems like the TX and TLs and RLs allows for a 128KB upgrade used solely for the video, but it does cause at least three games to fail.

  5. Great Hierophant:

    I don't know about the later 1000s with 16-bit CPUs, but there is one thing I distinctly remember about the original TX. I was a subscriber to 80 Micro magazine and they specialized in coverage of the Tandy Z-80 line and the Intel/PC compatible line. They ran the announcement of the TX as their cover story in the October 1987 issue. I have it in my hands as I write this. It says verbatim that the 286's data bus in the TX was purposely "clipped" to 8 bits in width (going to the DRAM). This was because, they said, that the TX was intended to be marketed as an XT compatible, in order not to compete with Tandy's AT-class computers (the Tandy 3000 and 3000HL, if memory serves).
    That's all I know.

  6. wiki leaker :

    80 Micro magazine didn't know what it was talking about. If the TX had a 286 tied to an 8-bit CPU bus would barely show any performance benefit over an SX. I know this for a fact because I have a 286 accelerator on an ISA card in my SX that uses 8KB of cache which can be turned off for compatibility reasons. When the cache is on, the SX's performance approaches a TX's, but when off the 286's is hobbled by the 8-bit data path to memory that the speed is barely faster than an 8088 at the same speed.

    Tandy had other ways than crippling the performance to distinguish the TX from the 3000 series. The TX has 10", 8-bit expansion slots, while the 3000 has 13" 16-bit slots.

  7. All the 3000 computers were AT compatible.

  8. Great Hierophant,

    Look inside your TX/TL. How many 16 bit slots do you count? In mine I count ZERO. why wouldn't they have put in full-width slots if the 286's 16 bit data bus is implemented ?? You could examine the 286/PCB and see where the A8-A15 address lines go, but that's a lot of work. If only somebody could produce the TX/TL Tech Manuals...

    If you still dispute the bus size, I suggest you take it up with the author of the T1000 entry on Wikipedia. Says right there the bus is implemented in 8 bits.

    Regarding the 80 Micro article: 1) it was actually the September 1987 issue, not October 2) the statement about the 8 bit bus implementation was not by the 80 Micro staff, but by the Tandy representative himself.

    I also know from experience that this is the sort of stunt our pals in the Tandy Towers are famous for...stunting one line of computers to preclude cannibalization of other lines. They purposely kept the TRS-80 Model 4 down to encourage new people to buy into T1000/MessDos.

  9. Wiki Leaker,

    I have read the TX and TL Technical Manuals, they are available in PDF form from here :

    The PCB connects all sixteen data lines to the onboard RAM and ROM That is a 16-bit memory data path. The schematics are quite clear.

    Tandy advertised the TX and TL as giving AT-class performance, which is not possible with an 8-bit memory data path to the RAM and ROM unless you have cache, and no 1000 machine has cache without a CPU accelerator.

    Tandy did not choose to provide the expansion slots with access to the 16-bit data path or the high address lines A20-A23, which does cripple the machine to some extent. In order to do that they would have had to add 36-pin extensions to the 62-pin slots and increase the length of the chassis. They would also have to add second DMA and IRQ controllers. This costs a lot more money. That issue of 80 Micro is not available in any online archive, so I cannot comment on what the Tandy representative said, but we all know that company spokesmen and Wikipedia authors are never wrong.

    Their next pricing tier would have been the 3000 series, which had full 16-bit compatible AT-style expansion slots and 13" for full length cards.

  10. I guess one other way the TLs are hobbled is that while the memory bus is 16-bit, the peripheral and DMA transfers are only 8-bit. Peripheral access probably not a big deal, but I suppose for a sound card the DMA could restrict things a bit.

  11. can you expand the memory of the tandy 1000 early to 1mb or beyond?

    if i use a make it 486 how does that change tandy 1000 tx ?