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Z88 MMC

SD cards are the best storage last few years. Widely used in cellphones, cameras, laptops and other devices. SD card seems to be a good storage for Z88 too.

I have designed Z88 MMC card as standard Z88 memory card for memory slots. Of course, case needs a small hole for inserting the SD card.
There is no IORQ signal on card's connector so port is mapped to memory area. Anyway, the Z88 has own WR signal with unstable address and data bus on falling edge of WR !!!

Port addressing:
A19=L
A18, A17=H
A13=H (top address bit of memory page)
ROE=L (RD)
WE=L (WR)
SEL=L
Port is inactive while Z88 tests standard cards.

Flash:
A19=H
ROE=L, or POE=L (RD)
WE=L (WR, Flash needs special unlocking sequence to erase or write data)
SEL=L

Two chips are used as an address decoder, one chip as input port and one as output port.
SD cards need 3.6V (or less), small voltage regulator is also on the board. Powering the card could be switched off.

Z88MMC
Prototype 3 boards

Card was designed as a hybrid card. Flash chip is optionally assembled to hold OZ or alternative OS.

PCB is 50mm long (standard cards are 52mm), it needs special case, data for 3D printer available.

BOM
 Mark Type Used as
 Socket
 IC1 SSF39SF040 512kB Flash
 PLCC32
 IC2 74HC00 /*
 address decoder
 SO14
 IC3 74HC32 /*
 address/op decoder
 SO14
 IC4 74LVC574 (LCX574) /*
 output port, 5V tolerant i/o
 S020W
 IC5 74HCT125 /*
 input port
 SO14
 IC6 MIC5504-3V3 low drop voltage regulator
 SOT23-6
 R1,2,3 10k pull-ups 0805
 R6, 7
 2k/2k5 /**
 LED current reducer
 0805
 C2,3,4,6,8 100n decoupling cap
 0805
 C1,5, 7
 1uF power stabilization
 0805
 T1 IRLF5203 SD power switch
 SOT23-3
 LED1, 2
 blue, red
 card operation sig.
 0805
 SD  microSD card socket
 
* prefer manufacturer with lower "Maximum Quiescent Supply" value noted in datasheet
** test before soldering, current depends on LED type and producer

Drawings, schematic, layout and software are subjects of intellectual property. Do not share, publish, produce or sell without author's permission.



At this moment, Z88MMC could be used with Z88 ROSE OS.
Thanks to Thierry, the last of the Z88 Mohicans, Z88MMC will be probably supported by OZ.

Z88 MMC in action



Z88MMC evolution

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