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46 lines
1.4 KiB
Markdown
46 lines
1.4 KiB
Markdown
# Writing to a AT28 EEPROM from a modern environment
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In this recipe, we'll build ourselves an ad-hoc EEPROM holder which is designed
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to be driven from an Arduino Uno.
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## Gathering parts
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* An Arduino Uno
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* A AT28C64B
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* 2 '164 shift registers
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* Sockets, header pins, proto board, etc.
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* [avra][avra] (will soon rewrite to Collapse OS' ASM)
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* avrdude to send program to Arduino
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## Schema
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This is a rather simple circuit which uses 2 chained '164 shift register to
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drive the AT28 address pins and connects CE, WE, OE and the data pins directly
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to the Arduino. Pins have been chosen so that the protoboard can plug directly
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on the Arduino's right side (except for VCC, which needs to be wired).
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PD0 and PD1 are not used because they're used for the UART.
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AT28 selection pins are pulled up to avoid accidental writes due to their line
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floating before Arduino's initialization.
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I've put 1uf decoupling caps next to each IC.
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## Software
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The software in at28wr.asm listens to the UART and writes every byte it receives
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to the AT28, starting at address 0. It expects tty-escaped content (see
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`/tools/ttysafe`).
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After having written the byte, it re-reads it from the EEPROM and spits it back
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to the UART, tty-escaped.
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## Usage
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After you've build and sent your binary to the Arduino with `make send`, you
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can send your (tty-safe!) content to your EEPROM using `/tools/pingpong`.
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[avra]: http://avra.sourceforge.net/
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