Electronics > Projects, Designs, and Technical Stuff
D8085AC ROM and 8279 finding keycodes
greenpossum:
It looks like the 8279 isn't set up to generate interrupts. The ret is just in case somehow the "impossible" happens, the 8085 will just resume what it was doing.
Also the RST line is just a common reset, both are input pins.
Dom87:
Doh! Thanks GreenPossum. That should have been obvious really.
To make more sense of what is going on in the program, I decided to have a look at how the databus and address lines are wired up to control each of the components on the main board.
Its by no means perfect, but I have created a flow diagram which I think illustrates what is going on.
and I think these are the address lines for each of the components.
I believe the program loops round and round in this section here, until either an IRQ is triggered or a key-press is loaded into the keyboard RAM, which is checked periodically.
--- Code: ---00AF L00AF: ; ###################### Main Program??? ####################
00AF : FB " " ei ; Enable Interrupt
00B0 : 3A 00 F9 ": " lda XF900
00B3 : E6 02 " " ani 002H
00B5 : CC C5 02 " " cz L02C5
00B8 : 3A 60 B6 ":` " lda XB660
00BB : E6 10 " " ani 010H
00BD : CA C9 00 " " jz L00C9 ; Jump if no key command in RAM?
00C0 : CD D2 00 " " call L00D2
00C3 : CD 10 01 " " call L0110
00C6 : C3 AF 00 " " jmp L00AF ; Repeat sub-routine
--- End code ---
Would I be right in believing that the E register is used for selecting the component address?
e.g.
mvi e,086H
mvi e,006H
mvi e,013H
Thanks!
duak:
It's been years, but I don't think so.
opcode 3A, LDA <address> reads the byte at memory location <address> into A
I think you would need:
opcode 1A, LDAX D reads the byte at the memory location pointed to by DE into A
Cheers,
greenpossum:
I assume you mean that the D register has been previously loaded with F8 and the E register is used to address the subunits enabled by U14. In that case you would be looking for 1A = ldax d like duak says, and its counterpart 12, stax d instructions.
westfw:
Does it look like the SDK-85 source code that you can still find commented listings for?http://bitsavers.trailing-edge.com/components/intel/8085/9800451A_SDK-85_Users_Manual_Jul77.pdf
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