/Tandy-EX-HX-3in1

Tandy 1000 EX/HX 3-in-1 Expansion Board

This is a single expansion board designed for the Tandy 1000 EX and HX computers, to include the following upgrades:

  • 640KB Base System Memory
  • 96KB Upper Memory
  • 16550-based DE9 Serial RS232 Port
  • XT-IDE based CompactFlash "Hard Drive"

Prerequisites

This board is for the Tandy 1000EX and 1000HX computers only. It will not work in any other computer model as it is. You must remove any expansion cards already in the computer, this is designed to be a single-board upgrade and has no provisions to allow for any other expansion cards.

Installing

This board plugs into the Tandy PLUS interface, and takes up "Slot 2" on the rear of the computer. Please be careful to align the PLUS bus connector before pushing down, to avoid bending pins on the computer. Secure the backplate to the computer with two screws. The IDE BIOS will automatically start and boot directly to the CF card on 1000EX machines. 1000HX loads a boot menu by default, and you will need to press F4 to load the IDE BIOS. If you want to bypass the Tandy DOS ROM and boot menu, run "SETUPHX" and change the "Primary Start-up Device" to "DISK" and press F1 to save.

Technical Details

This board has no configuration jumpers and is designed to be plug-and-play. The only jumper is to enable programming the ROM. Install the jumper to flash the XT-IDE BIOS, otherwise the jumper should be removed. All assembled boards and kits sold by me come with a pre-programmed ROM, and this jumper should be left empty.

The board is hardwired with these memory locations/ports:

SRAM:  0x0000-0x5FFF, 0xC800-0xDFFF
UART:  0x3F8, IRQ 4
IDE:   0x300
ROM:   0xC000-0xC7FF

Assembly Notes

All functions of the board are independent, no parts are shared between functions. If you do not want to use a specific function, you can safely omit any parts referenced with the function in the name (such as "232" for RS232).

Recommended assembly order: (Shortest to tallest)

  • 1 - Resistors (R1-R3, R4 for v1.8+)
  • 2 - Bypass Capacitors (C1-C16, only noted as "0.1uF" on the boards)
  • 3 - 74 series Chips (U1-4, U6-7, U9, U11-13)
  • 4 - ROM Socket (U5 Socket)
  • 5 - SRAM Chip (U10)
  • 6 - Oscillator (OSC1)
  • 7 - UART Socket (U8 Socket) - Pay very special attention to the orientation! See note below.
  • 8 - Connectors (BUS1, CF-J1, CF-J2, 232-P2)
  • 8a - Bodge Resistor on rear of board. (Only for Version 1.7a boards)
  • 9 - ROM and UART chips into their sockets.
  • 10 - CF Adapter
  • 11 - Backplate

NOTE: Please take careful note of part orientation. To optimize some trace routing, not all chips are oriented in the same direction. 232-U6, 232-U8, and RAM-U11 are all opposite oritentation than the other horizontal chips. Installing these backwards will destroy the chips. Pay special attention to 232-U8's socket, it must be installed with the "Pin 1 Arrow" installed facing towards the left of the board. 232-OSC1 is installed "upside down", with the squared corner facing the upper right.

Bill of Materials

Quantity Ref(s) Mouser Part Number Digikey Part Number Description
1 BUS1 200-CES13101SD
See Note2 Below		 SAM1084-31-ND
See Note2 Below		 2x31 2.54mm Header Socket
1 CF-J1 517-8540-4500PL 2x20 2.54mm Header Socket, 11mm height.
4 R1 through R4 603-CFR-12JT-52-10K 10kOhm Resistor
16 C1 through C16 594-K104M15X7RF53L2 0.1uF Multilayer Ceramic Capacitor, 2.5mm Lead Spacing
1 CP1 647-RNU1C101MDS1 100uF 16V Polymer or Electrolytic Capacitor, 2.5mm Lead Spacing
1 232-OSC1 774-MXO45HS-3C-1.8 110-MXO45HS-3C-1M843200-ND 1.8432Mhz 1/2-size Oscillator
1 232-P2 806-K22X-E9P-N-99 2092-K22X-E9P-N-ND DE9 Male Right Angle Connector
2 232-P2 Screw 571-5207953-3 SFSO4401NR-ND Jackscrew for DE9 connector
1 232-U6 595-GD75232N 296-GD75232N-ND GD75232N RS232 Driver
2 232-U7, 232-U9 595-SN74LS138N 296-1639-5-ND 74LS138 3-to-8 Line Demux
1 232-U8 701-ST16C550CJ44TR-F 1016-1259-5-ND 16550/16C550 UART in PLCC-44 Package
1 232-U8 Socket 517-8444-11B1-RK-TP 3M4411B1-ND PLCC-44 Through Hole Socket
1 CF-J2 200-CES10101TD 1x2 2.54mm Header Socket
1 CF-U1 595-SN74LS139AN 296-1640-5-ND 74LS139 Dual 2-to-4 Demux
2 CF-U2, ROM-U4 595-SN74LS688N
or 595-SN74F521N		 296-1667-5-ND 74LS688 or 74F521 8-bit Comparator
2 CF-U3, RAM-U11 595-SN74LS245N 296-1655-5-ND 74LS245 Tri-state Bus Transciever
1 RAM-U10 913-AS6C4008-55PCN 1450-1027-ND AS6C4008-55PCN 4mbit (512k x 8) Static RAM
1 RAM-U12 595-SN74LS00N 296-1626-ND 74LS00 Quad NAND Gate
1 RAM-U13 595-SN74LS32N 296-1658-5-ND 74LS32 Quad OR Gate
1 ROM-U5 556-AT28C64B15PU AT28C64B-15PU-ND 28C64 64k x 8 EEPROM
1 ROM-U5 Socket 517-4828-6000-CP ED3052-5-ND 28-pin Wide DIP Socket
1 CF-IDE Adapter n/a n/a CF to IDE Adapter from eBay or AliExpress (See note below)

Note: All 74LSxx series logic ICs can be substituted with any family with "LS" or "T" in the name, such as ALS, ACT, AHCT, or HCT among others.

Note2: For the BUS1 Connectors, I have many of these left over from my last order of custom connectors. You can buy them for $1/ea plus shipping. Even for one, it is far cheaper than the $13 that Mouser wants. Please email tandy.3in1@gmail.com to order.

BIOS

This board uses the XT-IDE Universal BIOS. I have included pre-configured images for 2.0.0B3 r602 (latest version as of the time of writing this). The 3in1BIOS-8088.zip will work on any EX or HX computer, and is the version that I preload on assembled boards and kits. I have also included a V20 Enhanced version for any EX/HX that has an NEC V20 (or clone) installed. This enhanced version will roughly double your disk speed, but only works on V20 machines.

CF-IDE Adapter

This board is designed a specific version of a CF-IDE adapter. They are widely available on eBay and AliExpress. It bears the mark of "IDE to CF Ver.D2". It can generally be identified by the metal cover over the CF card connector. I do not have a link to any one specific vendor or listing, but if the adapter includes the metal backplate and has a metal cover over the CF slot, then it should be correct.

The CF adapter does also need a few modifications, please refer to the "IDE Adapter Modifications.pdf" for details. It also has photos of the adapter for reference to buy the proper adapter.

If you have any questions, feel free to join the Discord server below and ask in the #tandy-3in1-support channel.

Support Discord

I have started a Discord server for more real-time technical support, as well as discussion for my various projects in progress. You can follow this link to join: https://discord.gg/QmFssyXnQt

Built With

Authors

License

This project is licensed under the Creative Commons - Attribution - ShareAlike 3.0 License

Attribution

This board was derrived from works by, uses design elements from, or contains sofware writen by the following:

README TO-DO

  • Assembly Instructions