Difference: MassStorage (21 vs. 22)

Revision 222019-02-10 - 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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A high-to-low transition on the CS pin is required to start an operation and a low-to-high transition is required to end an operation.

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Invalid Opcode: If an invalid opcode is received, no data will be shifted into AT25M02 and the Serial Data

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Invalid Opcode: If an invalid opcode is received, no data will be shifted into AT25M02 and the Serial Data

Output (SO) pin will remain in a high impedance state until the falling edge of CS is detected again. This will reinitialize the serial communication.

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