Ace Board 3 EXP.
The main thrust of my work at the moment it on ACE3NOKB which includes some significant changes to use more modern components and fully populate the RAM as well as make some space for extra ROM. Included on the board is a Zilog KIO Z80C90 chip. This means that there will have to be a change in the interrupt structure which requires the extra ROM. It is all here but is ongoing work so less than 0 guarantees are provided.
As you can see I've moved to PLCC for the Z80, which is the larger of the 2 brown sockets. The smaller socket contains NOR-Flash memory which will help in development by allowing me to update the firmware.
The large empty socket is for the Zilog KIO this provides 2 serial channels, 24 GPIO pins and 3 CTC, one of which will handle the 50hz interrupt this will entail a move to interrupt mode 2. To create space for the extra ROM I've moved the start of the system RAM up 1k so that the 4k between 12k and 16k can be used. The 2 chips next to the ROM socket are the RAM 64k in total, of which 48 will be available.
In the bottom left there are a collection of pins and sockets that I will be able to use to reconfigure the clock without getting a new board. The first test will be to try the overclock suggestion from Edwin Blink using the original crystal speed, this might double the speed of the CPU. It may be possible to test up to 13Mhz though the ZIO is only rated to 10.
The problem is that the clock speed to the video is derived from the CPU clock and must be obtainable with division by 2 from the CPU clock. In later boards, I will add a second clock to remove this limitation but that make require dual-ported RAM, though that would have the advantage of preventing contention between the CPU and Video hardware, so speeding up the system. It would also simplify some of the design that arbitrates access but they are big and expensive.
The work with ZIO will be useful with any Z180 or eZ80 version as they contain mostly the same items but are clocked at a higher speed so it should b possible to get 8 times the speed, 26 Mhz, with a Z180 and a single clock and 32 with the split clock/dual-ported RAM.
The large empty socket is for the Zilog KIO this provides 2 serial channels, 24 GPIO pins and 3 CTC, one of which will handle the 50hz interrupt this will entail a move to interrupt mode 2. To create space for the extra ROM I've moved the start of the system RAM up 1k so that the 4k between 12k and 16k can be used. The 2 chips next to the ROM socket are the RAM 64k in total, of which 48 will be available.
In the bottom left there are a collection of pins and sockets that I will be able to use to reconfigure the clock without getting a new board. The first test will be to try the overclock suggestion from Edwin Blink using the original crystal speed, this might double the speed of the CPU. It may be possible to test up to 13Mhz though the ZIO is only rated to 10.
The problem is that the clock speed to the video is derived from the CPU clock and must be obtainable with division by 2 from the CPU clock. In later boards, I will add a second clock to remove this limitation but that make require dual-ported RAM, though that would have the advantage of preventing contention between the CPU and Video hardware, so speeding up the system. It would also simplify some of the design that arbitrates access but they are big and expensive.
The work with ZIO will be useful with any Z180 or eZ80 version as they contain mostly the same items but are clocked at a higher speed so it should b possible to get 8 times the speed, 26 Mhz, with a Z180 and a single clock and 32 with the split clock/dual-ported RAM.
Comments
Post a Comment