Custom ROM WBW

I am a big fan of retro homebrew computers. I have a few kits that I ordered from Tindie.com based on the RC2014 model (SC126). To keep it completely retro, I bought a classic amber terminal so I could have that classic user experience. After a few hours of troubleshooting, I determined that the default baud rate on the computer (115,200) was too fast for the terminal. I had to find a way to slow it down.

After posting to the retro-comp Google group, the kind people there helped me solve my problem. It turns out that I can reconfigure the default baud rate of the serial ports from within a configuration file. This blog post is my written record of what I had to do, as I will have to perform this procedure after each ROMWBW update.

  • Update /ROMWBW-[Version]/Source/HBIOS/cfg_scz180.asm
    • Typically, this file would not be modified, but Wayne informed me of a functional quirk of ROMWBW that requires that this file be modified
    • The line that reads
      • DEFSERCFG .EQU SER_115200_8N1 | SER_RTS ; DEFAULT SERIAL LINE CONFIG (SEE STD.ASM)
      • Should be changed to:
      • DEFSERCFG .EQU SER_19200_8N1 | SER_RTS ; DEFAULT SERIAL LINE CONFIG (SEE STD.ASM)
  • Return to the base directory for ROMWBW
  • run make to build the OS
  • Once finished, find the correct binary for your computer
    • Mine was /Binary/SCZ180_sc126.rom (created using the configuration changes made above)
  • Burn the .rom file to EEPROM
    • I am using the TL866II Plus
    • I am using minipro on macOS
      • Install minipro (brew install minipro)
      • run minipro
        • You may receive an error about libusb not being safe
        • Open Settings on your Mac and navigate to Privacy and Security
        • Scroll down to Security. You should see a warning about libusb. Enable it
      • I use minipro --device "SST39SF040" -w SCZ180_sc126.rom to burn the rom image
  • Install ROM into the socket on the computer

I am using SST 39SF040 EEPROMs. I have found them to be easy to work with.

Once I installed the EEPROM into the computer, I was able to hook the terminal up to the serial port on the computer. It works well at 19,200 baud. Since the SC126 has another serial port, I use that one to connect to my computer to transfer programs that I write on my Mac (using VSCode and z88dk) over to the retro computer.

To transfer a program to the retro computer from my mac, I use the serial program. To send the file, I choose File-SendFile and select the .bin file from the project folder. I then select XMODEM and make sure that the 1K Block Size is checked.

On the retro computer, I change drives to D:. Then, type B:XM R1 FNAME.COM. I switch back to the Mac and click the Send button.

XM is short for XMODEM. The R1 indicates that we’ll use the second serial port on the SC-126. I have an amber terminal monitor on Serial port 0 that I use to control the computer.