All posts by Joseph Knowles

Z-80 Homebrew MkII

I need to come up with a good name for this project… Anyhow, after my previous prototype I have decided to built a Z-80 project anew. Basically, the issue with the previous was lack of UART (I built one, had it working, then accidentally blew it up), the different boards and the masses of wires making the computer unstable and legs of my flash ROM getting bent from too much insertion and removal.

Therefore, this one will all be on the same board, have custom sockets for expansion and a built in UART. I will also add a ZIF socket to handle my ROM issues.

Furthermore, I plan to add some paging to the memory, so that I can page the ROM in and out; but this isn’t finalised yet.

All I have done so far is build a power supply to regulate the output from a transformer down to the 5V needed for the CMOS logic, but you need to start somewhere…

Start of a new computer, just a 7805 regulator.
Start of a new computer, just a 7805 regulator.

It’s alive! Z-80 Computer hardware now complete.

I have just finished assembling the memory board of my Z-80 homebrew project. All components individually tested, I placed the test program on the ROM, inserted the Z-80 and it worked first time!

It's Alive: Z-80 Homebrew
It’s Alive: Z-80 Homebrew

There is still a little more to do on modifying the I/O board to run the monitor program (which also needs writing) as the board was designed to test the various different circuits. However, the computer successfully executes the following test routine:

;COMPUTER TEST ROUTINE
;
;OUTPUTS ON PORT 0 ANY INPUT ON PORT 0 WHILST CALLING AN EMPTY SUBROUTINE
;
;

LD SP,9000H

L1: IN A,(00H)
CALL TEST
OUT (00H),A
JP L1
TEST RET

This outputs on port 0 any input on port 0 whilst using the stack pointer to save the value of the program counter in the RAM for the execution of an empty subroutine. Thus the I/O, ROM and RAM are all tested. Monitor listing to come soon no doubt.

Z-80 Update

Z-80
Z-80 home brew board
Progress on Memory Board
Progress on Memory Board

Unfortunately, it has been a long time since I could work on my  Z-80 homebrew; it has been in storage for many months. However, my setup is active once more and I have built the processor board. It consists of a power supply, clock, reset logic and buffers for the data, address and control busses. Unlike the I/O board, whose schematic is only in my head, I have used KiCad to design the circuitry and I will upload that separately.

On a separate board lives the I/O decoding and memory, on which I’ve made a start (see picture above). It’s all designed for easy testing and expansion, hence all the chips are socketed. I’ll update soon with the schematics and pictures of the finished article!

 

Gesualdo in the Twentieth Century

My new book chapter, ‘Gesualdo in the Twentieth Century’, has now been published in Critical Music Historiography: Probing Canons, Ideologies and Institutions and is available from Ashgate. It is based on a 2011 conference paper I gave at the Radical Music History symposium at the Sibelius Academy in Helsinki.

View on Ashgate’s website here.

Critical Music Historiography