NEO-ZMC

Memory Controller. Handles the Z80 bankswitching in cartridges. To save pins, the Z80's upper address line are also used as data input. The chip's write strobe SDRD0 is port address decoded inside the system.

=Pinout=

Pins 10, 11, 12 may be M1 higher address bits ?


 * SDA0, SDA1, SDA8~15: Z80 address bus
 * M1 A11~M1 A18: M1 ROM address lines
 * SDRD0: Decoded write signal from (latch on rising edge)

=Operation=

SDA8~SDA15 are used for the bank number (data), SDA0 and SDA1 for selecting the window.

Details


SDRD0 must be high before configuring banks.

To configure a bank to be accessed (e.g. bank 1 in the $8000~$BFFF range):
 * Set SDRD0 low (prepare for new bank configuration, outputs are tri-stated)
 * Set SDA0~15 = $8103, select 16KiB bank 1 in window 3 (Why $8103 and not just $0103 ?)
 * Set SDRD0 high (latch bank, ready to convert inputs to proper output signals)
 * Now, when the Z80 reads the $8000~BFFF range, NEO-ZMC will map this to the M1 ROM zone $04000~$07FFF