PicoMEM Boot and EMS Support: Tandy 1000 RL/RLX/TL BIOS Mods

[Cloudschatze]

Here are a couple of additional Tandy 1000 BIOS modifications, this time shifting the external boot ROM range that normally starts at CA80h in the RL, RLX-A/B, TL/2, and TL/3 systems to CA00h. By so doing, a card such as the PicoMEM can then be booted from that address, freeing-up the entire D000h-DFFFh range for EMS or UMBs.

The RLX modifications also include a VGA BIOS update, and, for the RLX-B specifically, the disabling of the internal ROM drive (as needed by both the PicoMEM and XUB-based cards).

You'll need a 27C400 or compatible EPROM (200ns or better) to write the relevant BIOS image to. If using a TL866 device, you'll also need an appropriate adapter. Take note of the position of the 40-pin ROM in its 42-pin socket before and after.


Tandy 1000 RL BIOS ROM Version 02.00.01
Original: 8079073.BIN
Modified: 8079073_CA00.BIN

• Allows booting from CA00h

Tandy 1000 RLX-A BIOS ROM Version 02.00.00
Original: 8049021.BIN
Modified: 8049021_CA00_VGA1-BIOS-VER-D-1.00-07.BIN

• Allows booting from CA00h
• VGA BIOS Version D, 1.00.07

Tandy 1000 RLX-B BIOS ROM Version 02.00.00
Original: 8079074.BIN
Modified: 8079074_NOROMDRIVE_CA00_VGA1-BIOS-VER-D-1.00-07.BIN

• Allows booting from CA00h
• Disables ROM drive
• VGA BIOS Version D, 1.00.07

Tandy 1000 TL/2 BIOS ROM Version 02.00.00
Original: 8079044.BIN
Modified: 8079044_CA00.BIN

• Allows booting from CA00h

Tandy 1000 TL/3 BIOS ROM Version 02.00.00
Original: 8079072.BIN
Modified: 8079072_CA00.BIN

• Allows booting from CA00h

 

[ralphmaif]

This is awesome. Thank you!

 

[ssthomas]

Hello would you be able to write me an eeprom if I provided the proper 27C400 for the TL/2? I wold need your 80790444_CA00.BIN due to the fact that I'm running a Picomem and I cannot access the extended memory due to exactly what you said the eeprom taking up the d0000 range. I could pay you for your time it just seems more of a viable option if it's economically feasible instead of buying an eprom programmer and doing it myself.

 

[carnch]

I'm new to this and from everything I've seen, the TL/3 has two ROM chips, an even and an odd. If I burn the modified ROM, which chip does it replace or do I need to replace both?

 

[ralphmaif]

I'm new to this and from everything I've seen, the TL/3 has two ROM chips, an even and an odd. If I burn the modified ROM, which chip does it replace or do I need to replace both?

Does your TL/2 have both of those banks populated? They are empty in my TL/3 which uses the 27C400 bank for BIOS instead.