Z80 Project Mark 2: Flashing lights progress
Last updated: 20 Sep 2009 - 17:38
I have made some progress on the Z80 project. Another mod, some software and learned some new lessons about PIC programming on Linux.
Another Mod I realised the other day that my plan to start testing peripherals with the PIC before inserting the Z80 would not work. My design has bus buffering to ensure the mash up of TTL and CMOS components all get valid signals. However the decision about what chip is driving the bus is made based on the status of the BUSACK line from the Z80. This means that without the Z80 fitted, or with it held in RESET the two sets of bus drivers (one from the Z80 and one from the PIC) could be in conflict as their enable line states are undefined. To deal with this problem I've added a 10K pull down resistor under the Z80, this will make sure that if the Z80 isn't driving the pin (because it's not fitted or it's in reset) the PIC has control of the data bus.
Software The first bit of software I wrote was a trivial