Hi,
I want to use the external IO bus to communicate with an FPGA using port A for the data bus and 6 bits from port B and two from port D for an 8 bit address bus. I will use the IOWR & IORD and use an IO strobe as a chip select to latch data into the FPGA.
I was wondering why the IO strobe has an 8K address space when the maximum number of address bits that can be used is 8 (256)?
Thanks
The I/O strobe has 8K address space because it was possible on the Rabbit 2000 (and later devices) to use the actual address and data bus for memory-mapped I/O. If you look at the schematic for the RCM2200 (for example), you’ll see the Realtek Ethernet controller connected to D0-D7 and A0 to A4.
The Rabbit 3000 introduced the option of an external I/O bus using Port A for data and 6 bits of Port B for addressing. My guess is that most memory-mapped I/O devices of the time had a limited number of registers so there wasn’t a need for an additional 16-bit address bus.
Thanks Tom. I figured you would be able to clear up this issue for me!
Terry