NEO-ZMC

NEO-ZMC chip on a MVS cartridge. Picture courtesy of [MVS-Scans].

Z80 memory controller. Has a hardwired 32KiB bank and switchable 16/8/4/2KiB banks arranged as a register file. To save pins the high address lines (A15-A8) are used for data input. The chip's write strobe is (port) address decoded inside the console.

Pinout

File:Neo-zmc pinout.png

OpenOffice Draw file: File:Neo-zmc.odg

• SDA0,SDA1,SDA8~15: Z80 address bus
• SDRD0: /Write signal from NEO-D0

Operation

SDA10,SDA9,SDA8 are bank selector and SDA1,SDA0 range size selector or rom size selector.

SDA1,SDA0 = 0,0 (Z80 port 8) select bank ranges for the Z80 $F000~$F7FF range (2Kbytes) (64k M1)

SDA1,SDA0 = 0,1 (Z80 port 9) select bank ranges for the Z80 $E000~$EFFF range (4Kbytes) (128k M1)

SDA1,SDA0 = 1,0 (Z80 port A) select bank ranges for the Z80 $C000~$DFFF range (8Kbytes) (256k M1)

SDA1,SDA0 = 1,1 (Z80 port B) select bank ranges for the Z80 $8000~$BFFF range (16Kbytes) (512k M1)

SDRD0 is the /write signal: the bank configuration is latched and the address output lines are changed on the rising edge.

Details:

SDRD0 must be high before configuring banks.

To configure a bank to be accessed (e.g. bank 0 in the $8000~$BFFF range):

• Set SDRD0 low (prepare for new bank configuration, outputs are tri-stated)
• Set SDA0~15 = $8003 (select bank 0 and 16k range size) Why $8003 and not just $0003 ?
• Set SDRD0 high (latch bank, ready to convert inputs to proper output signals)
• Now, when the Z80 accesses the $8000~BFFF range, NEO-ZMC will convert this the M1 ROM zone $00000~$03FFF;

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 bank 1 and 16k range size) Why $8103 and not just $0103 ?
• Set SDRD0 high (latch bank, ready to convert inputs to proper output signals)
• Now, when the Z80 accesses the $8000~BFFF range, NEO-ZMC will convert this the M1 ROM zone $04000~$07FFF;

To configure a bank to be accessed (e.g. bank 3 in the $C000~$DFFF range):

• Set SDRD0 low (prepare for new bank configuration, outputs are tri-stated)
• Set SDA0~15 = $8302 (select bank 3 and 8k range size) Why $8302 and not just $0302 ?
• Set SDRD0 high (latch bank, ready to convert inputs to proper output signals)
• Now, when the Z80 accesses the $C000~DFFF range, NEO-ZMC will convert this the M1 ROM zone $06000~$07FFF;

Z80 address bus (SDA0~15)	BANK 0-31	Window...	...mapped to (M1 A0~18)
$8003	bank 00	$8000~$BFFF	$00000~$03FFF
$8103	bank 01	$8000~$BFFF	$04000~$07FFF
$8203	bank 02	$8000~$BFFF	$08000~$0BFFF
$8303	bank 03	$8000~$BFFF	$0C000~$0FFFF
$8403	bank 04	$8000~$BFFF	$10000~$13FFF
$8503	bank 05	$8000~$BFFF	$14000~$17FFF
$8603	bank 06	$8000~$BFFF	$18000~$1BFFF
$8703	bank 07	$8000~$BFFF	$1C000~$1FFFF
$8803	bank 08	$8000~$BFFF	$20000~$23FFF
$8903	bank 09	$8000~$BFFF	$24000~$27FFF
$8A03	bank 10	$8000~$BFFF	$28000~$2BFFF
$8B03	bank 11	$8000~$BFFF	$2C000~$2FFFF
$8C03	bank 12	$8000~$BFFF	$30000~$33FFF
$8D03	bank 13	$8000~$BFFF	$34000~$37FFF
$8E03	bank 14	$8000~$BFFF	$38000~$3BFFF
$8F03	bank 15	$8000~$BFFF	$3C000~$3FFFF
$9003	bank 16	$8000~$BFFF	$40000~$43FFF
$9103	bank 17	$8000~$BFFF	$40000~$47FFF
$9203	bank 18	$8000~$BFFF	$40000~$4BFFF
$9303	bank 19	$8000~$BFFF	$40000~$4FFFF
$9403	bank 20	$8000~$BFFF	$50000~$53FFF
$9503	bank 21	$8000~$BFFF	$54000~$57FFF
$9603	bank 22	$8000~$BFFF	$58000~$5BFFF
$9703	bank 23	$8000~$BFFF	$5C000~$5FFFF
$9803	bank 24	$8000~$BFFF	$60000~$63FFF
$9903	bank 25	$8000~$BFFF	$64000~$67FFF
$9A03	bank 26	$8000~$BFFF	$68000~$6BFFF
$9B03	bank 27	$8000~$BFFF	$6C000~$6FFFF
$9C03	bank 28	$8000~$BFFF	$70000~$73FFF
$9D03	bank 29	$8000~$BFFF	$74000~$77FFF
$9E03	bank 30	$8000~$BFFF	$78000~$7BFFF
$9F03	bank 31	$8000~$BFFF	$7C000~$7FFFF

Others range sets may differ from the range access here.(e.g. $8000, $8001 or $8002)