Difference: MassStorage (20 vs. 21)

Revision 212019-02-10 - PeterSchmid

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SPI EEPROMs

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The Serial Peripheral Interface SPI

or four-wire serial bus is easy to use. The CDP1802 (MC) is the SPI master, the EEPROM is the slave. There are many different EEPROM types and sizes available e.g. AT25M02

(2Mbit, 256 KiB, $3), 25LC1024

(128 KiB, $2), or 25LC512

(64 KiB, $1.50). All available in DIL8 packages. 64/128/256 KiB seems very small for today's standards where storage is quantified in GiB, but I think it's more than enough for a small Forth system, the size is similar to early floppy disks. If you want more memory there are 16 MiB serial Flash chips e.g. from WINBOND W25Q128J

or IS25LP128F

, please note they are 3.3 V devices and in SMT!

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The Serial Peripheral Interface SPI

or four-wire serial bus is easy to use. The CDP1802 (MC) is the SPI master, the EEPROM is the slave. There are many different EEPROM types and sizes available e.g. !AT25M02

(2Mbit, 256 KiB, $3), 25LC1024

(128 KiB, $2), or 25LC512

or IS25LP128F

, please note they are 3.3 V devices and in SMT!

CLK   MC ->- host
MOSI  MC ->- host

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about 230 cycles for one byte -> 1 ms -> 1 KiB takes about 1 s @ 1.79 MHz

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about 230 cycles for one byte -> 1 ms -> 1 KiB takes about 1 s @ 1.79 MHz

Write Byte

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BNZ RDBITLOOP

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about 200 cycles for one byte -> 1 ms -> 1 KiB takes about 1 s

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about 200 cycles for one byte -> 1 ms -> 1 KiB takes about 1 s

Write Byte

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EEPROM Connected to Raspberry Pi

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I use a Raspberry Pi Zero (about $20) as an EEPROM programmer.

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Mini Boot Loader

For RAM only Membership Cards you need some kind of bootstrap loader. To type in a monitor or even BASIC or FORTH is nearly impossible. Serial EEPROMs in DIP8 packages are cheap and easy to get. But you still have to use the front panel to type in the boot loader itself (this is the first-stage boot loader).

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The "patched on MC PCB" boot loader takes about 25 s for 32 KiB, the DB25 variant takes about 29 s. For the sources see https://github.com/spyren/RaspiElf/tree/master/eeprom

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The "patched on MC PCB" boot loader takes about 25 s for 32 KiB, the DB25 variant takes about 29 s. For the sources see https://github.com/spyren/RaspiElf/tree/master/eeprom

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