vprada
Experienced Member
An article I read about the QC-11, the Japanese version of the QX-11, stated that the QC-11 came with 128KB of ROM. The export QX-11, however, comes with two 32KB ROM chips, for a total of 64KB of ROM.
While doing some reverse engineering around one of the gate arrays installed in the QX-11, I found a set of jumpers labeled J1, J2, and J3. I discovered that these three jumpers allow you to change the expected size of each of the QX-11 ROM chips. Based on what I found, the machine can support 16KB, 32KB, or 64KB ROM chips.
Changing the jumper positions changes how the address lines for each 27256 ROM chip are connected. Position B on each jumper ties the corresponding 27256 address line to 5V. Position A ties the ROM address line to the system address lines A14 or A15.
Having the option to install a 64KB ROM allowed me to add additional utilities that are available immediately at boot time. These utilities have proven to be very useful, especially when restoring a QX-11 without any QX-11-formatted disks, or when there is no easy way to create new floppies from disk images.
I created a detailed post in my QX-11 github but long story short, my new rom includes FORMAT.COM, FILINK.COM and MODE.COM, to basically format new floppies with the native QX-11 format, transfer files from a modern system to the QX-11 via serial port, and mode to change the default speed for the serial port.
While doing some reverse engineering around one of the gate arrays installed in the QX-11, I found a set of jumpers labeled J1, J2, and J3. I discovered that these three jumpers allow you to change the expected size of each of the QX-11 ROM chips. Based on what I found, the machine can support 16KB, 32KB, or 64KB ROM chips.
Changing the jumper positions changes how the address lines for each 27256 ROM chip are connected. Position B on each jumper ties the corresponding 27256 address line to 5V. Position A ties the ROM address line to the system address lines A14 or A15.
Having the option to install a 64KB ROM allowed me to add additional utilities that are available immediately at boot time. These utilities have proven to be very useful, especially when restoring a QX-11 without any QX-11-formatted disks, or when there is no easy way to create new floppies from disk images.
I created a detailed post in my QX-11 github but long story short, my new rom includes FORMAT.COM, FILINK.COM and MODE.COM, to basically format new floppies with the native QX-11 format, transfer files from a modern system to the QX-11 via serial port, and mode to change the default speed for the serial port.