19-01-2022, 01:52 AM
PAD 35 shouldn't be connected to IC28 PIN 1 as IC28 is only associated with bank selection of the PAK ROM's residing at C000h.
PAD 35 should go to IC 26 PIN 5 which is the upper bank selection of a 27128 (if fitted) to ROM D location (NET ROM).
This bank selection uses a little known function of the Z80 where it places the contents of the A register out onto the upper Byte of the Address Bus when doing an INPUT command from a Port. After reset it is always reset to the first 4KB (32kb)
Chapter 4 - Coreboard description in the Technical Manual gives an example of how to access the four 32kb banks of the NET ROM location.
LD A,2 (note this is either 0,1,2 or3 depending on which bank you wish to launch, 2 & 3 are the upper half of the 27128 EPROM.)
IN A,0Ah (Port #10)
JP NET
The PC85 uses the two lower banks 64kb for TELCOM, Calculator, Self Test & MONITOR (I believe it is a different monitor to the one in the WORDBEE ROM).
However I have yet to find a program designed to go into the upper 64kb of the NET ROM location.
Just about any 4KB programs that are compiled to run from the E000h location and don't need access to any of the other programs listed above.
Hope this helps.
Ernest
PAD 35 should go to IC 26 PIN 5 which is the upper bank selection of a 27128 (if fitted) to ROM D location (NET ROM).
This bank selection uses a little known function of the Z80 where it places the contents of the A register out onto the upper Byte of the Address Bus when doing an INPUT command from a Port. After reset it is always reset to the first 4KB (32kb)
Chapter 4 - Coreboard description in the Technical Manual gives an example of how to access the four 32kb banks of the NET ROM location.
LD A,2 (note this is either 0,1,2 or3 depending on which bank you wish to launch, 2 & 3 are the upper half of the 27128 EPROM.)
IN A,0Ah (Port #10)
JP NET
The PC85 uses the two lower banks 64kb for TELCOM, Calculator, Self Test & MONITOR (I believe it is a different monitor to the one in the WORDBEE ROM).
However I have yet to find a program designed to go into the upper 64kb of the NET ROM location.
Just about any 4KB programs that are compiled to run from the E000h location and don't need access to any of the other programs listed above.
Hope this helps.
Ernest