Hi --
Having trouble getting the Z80 CPU card going. Trying to run at 4MHz with a Z80B CPU (known good, runs in another CPU card at 4 MHz just fine). Using a 27C32B EPROM (supposed to be easily fast enough to function at 4MHz). No wait states selected (all dip switches off). 24-pin EPROM is installed in the 28-pin socket with 4 vacant pins visible at the notch end of the chip (I hope that's right). With an EPROM full of HALT's (76h), at power up OE of the EPROM wiggles for a time, and then goes (and stays) high. Same for pin 18 (/HALT) of the CPU. Chassis reset does NOT do anything at this point. The ROM LED comes on at power up, but then goes off after a short while (maybe a minute). Reset does not change the status of the LED -- only a power cycle does.
I expected to see just the opposite behavior, i.e. the ROM LED is dark at power up, and stays that way for an instant until the EPROM gets found, and then it goes on, and stays on. Same with OE on the EPROM -- high at
first and then wiggles as the EPROM is executed.
Clocks from 4 MHz and 2 MHz oscillators seem fine.
Any ideas about what's wrong?
Jumpers:
*p37*
o o
|
o o
*p36*
o o
o-o
o o
p3 no jmprs installed
*p2*
o o
o o
o-o
o o
*jp4&5
o o
|
o o
*jp7*
o-o
o-o
*k2*
o
|
o
o
*p4*
o o
| |
o o
*p39*
o o
o o
o-o
*jp8&9
o
o
o |
| o
o
I think these are set just the way they are shown in the photos on the Web page?