Hi all,
So with all this free time on my hands (Well, I have some free time now
), I have decided to revisit the million Z80 projects that I have attempted. Now in the past I never get past the hardware part of the project. In other words I build a z80 machine that works but never write the software for it (or even complete it).
So this time I have decided to finally stick to something and following it all the way to the end. But there will be a spin on this machine unlike the others in the past. The hardware that I used to design was advanced for a Z80 (such as parallelism, multi-tasking, keyboard input with serial HDs), and this is probably why it never went futher. This time however I am making a 70's style mainframe computer!
This machine will have simplicity in its heart (and I MEAN simplicity). The computer will be built in mini racks witch each rack card being 3x2 inches for IO and (most likely), 4 x 3 inches for the motherboard cards.
Front Panel
Taking inspiration from IBM mainframe machines this is the front panel (so far...)
Single step clocking and full speed will be included soon.
Keyboard Input
This card has already been designed and I plan to get four made. Huh, 4? That's right! Most people use toggle switches for simple machines but that just does not work for me at all! What I am doing instead is using toggle flip flops with their toggle input connected to tactile switches. This way the switching mechanism is electronic (and thus can be manipulated by the CPU). So each card can accept up to 8 input buttons, one clear button (to clear all the latches), and one NMI button. The NMI button when pressed forces the processor to jump to a subroutine which halts the current program. This way, the system can be restored without a hardware reset.
Display Input
Inspired by the MK14 Science of Cambridge I will be utilising 8 7-segment displays. This card also fits into the IO rack measuring just 3x2 inches. Two registers are used to show a specific portion of the display which means that a subroutine will need to be fired every so often to refresh the display. Therefore a 50Hz signal will be fed into the INT pin (giving the user the choice to shut off the display).
The display itself will consist of 8 7-segment digits, all the control signals, data bus and address bus. So imagine many blinky lights!
Paper Tape Reader
Yes, a paper tape reader. What 70's style computer would not have one! The tape will have one clock line (for data clocking), 4 data lines and one data ready clock line. Every two groups of 4 bit data will be clocked in before the data ready line is read. This will also fit onto a 3x2 inch card and will make up the 5th card in the IO rack.
Processor Core
This will be the most boring card as it will just house the Z80, a tiny 2K ROM and two 32K chips which will be used to give in total 62K RAM. The ROM will hold a primitive monitor program that will just enter data into memory and enable a RUN mode. The plan is to create a system that just sits there until an external system (such as an other computer), sends it a request to run. So like a mainframe computer it would then do the calcs and return the data when ready. I know that it would have the power of a real mainframe but I though that it would be a neat thing to have on my desk!
Something that I would like to think of is getting some kind of LAN connection so that remote computers could use it but I would have to think how to implement it.
So until I can think of other things that this machine will have that is the goal!
Any suggestions would be fantastic but remember, its gotta be old
So with all this free time on my hands (Well, I have some free time now
), I have decided to revisit the million Z80 projects that I have attempted. Now in the past I never get past the hardware part of the project. In other words I build a z80 machine that works but never write the software for it (or even complete it).So this time I have decided to finally stick to something and following it all the way to the end. But there will be a spin on this machine unlike the others in the past. The hardware that I used to design was advanced for a Z80 (such as parallelism, multi-tasking, keyboard input with serial HDs), and this is probably why it never went futher. This time however I am making a 70's style mainframe computer!
This machine will have simplicity in its heart (and I MEAN simplicity). The computer will be built in mini racks witch each rack card being 3x2 inches for IO and (most likely), 4 x 3 inches for the motherboard cards.
Front Panel
Taking inspiration from IBM mainframe machines this is the front panel (so far...)
Single step clocking and full speed will be included soon.
Keyboard Input
This card has already been designed and I plan to get four made. Huh, 4? That's right! Most people use toggle switches for simple machines but that just does not work for me at all! What I am doing instead is using toggle flip flops with their toggle input connected to tactile switches. This way the switching mechanism is electronic (and thus can be manipulated by the CPU). So each card can accept up to 8 input buttons, one clear button (to clear all the latches), and one NMI button. The NMI button when pressed forces the processor to jump to a subroutine which halts the current program. This way, the system can be restored without a hardware reset.
Display Input
Inspired by the MK14 Science of Cambridge I will be utilising 8 7-segment displays. This card also fits into the IO rack measuring just 3x2 inches. Two registers are used to show a specific portion of the display which means that a subroutine will need to be fired every so often to refresh the display. Therefore a 50Hz signal will be fed into the INT pin (giving the user the choice to shut off the display).
The display itself will consist of 8 7-segment digits, all the control signals, data bus and address bus. So imagine many blinky lights!
Paper Tape Reader
Yes, a paper tape reader. What 70's style computer would not have one! The tape will have one clock line (for data clocking), 4 data lines and one data ready clock line. Every two groups of 4 bit data will be clocked in before the data ready line is read. This will also fit onto a 3x2 inch card and will make up the 5th card in the IO rack.
Processor Core
This will be the most boring card as it will just house the Z80, a tiny 2K ROM and two 32K chips which will be used to give in total 62K RAM. The ROM will hold a primitive monitor program that will just enter data into memory and enable a RUN mode. The plan is to create a system that just sits there until an external system (such as an other computer), sends it a request to run. So like a mainframe computer it would then do the calcs and return the data when ready. I know that it would have the power of a real mainframe but I though that it would be a neat thing to have on my desk!
Something that I would like to think of is getting some kind of LAN connection so that remote computers could use it but I would have to think how to implement it.
So until I can think of other things that this machine will have that is the goal!
Any suggestions would be fantastic but remember, its gotta be old
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