hi all friends,

i'm back again like a clown to make you happy with my Z80 tests for dummy peple :) (you can put up some cartoon if you want but pay me something if it works)

till monday i cannot program any eprom..

i made an attempt to simulate a JP HL instruction. It is a single byte instruction. This becouse i would just have address bus fixed to a value. So i've prepared the JP HL instruction in a soket. But nothing, it dont work, the address bus rest in a strange state, some pin to 1,8V others to 2,2 etc etc, that coul be a medium value of continuosly PC increment. I was expecting a 0 for all 16bits....
Posted on 2004-01-10 10:00:29 by Bit7
I missed this post.

See my comments in the Z80, Eprom thread.

The 1.8 and 2.2 (this is measured with an oscilloscope, right?) is probably due to noise on a floating BUSREQ pin. You need to pull up BUSREQ, WAIT, INT, and NMI. I would normally use resistors, as it allows future connections.

I suggest using 00 000 000 (NOP) to get an incrementing address bus. The op code cycle will insert a RAM refresh address, so every second address will be the instruction address. It will be difficult to see if the address is changing properly with a single channel scope.
Posted on 2004-01-10 18:14:08 by tenkey
As you are not likely to get small DRAMs any more, you can use the /WAIT signal to single step (or more precisely, single cycle) the Z80.

To do this, you need a circuit that will hold /WAIT low until you press a switch. When the switch is pressed, the /WAIT line is pulsed for one clock cycle, rising edge to rising edge. The Z80 will sample the /WAIT line on the falling edge and finish the memory or I/O cycle. Because the /WAIT line will be back to low when it is sampled again, the Z80 will enter the wait state on the next memory or I/O cycle with stable address, data, and control lines.

To run the Z80 at full speed, you need to allow /WAIT to stay high.
Posted on 2004-01-10 18:51:09 by tenkey