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→Verification Process
= Code Verification =
== Verification Process ==
The process to read back code from the 87C51's EPROM memory is described in the NXP datasheet (in the EPROM Characteristics section). However, there's a lot of info in this section about ''writing'' to the EPROM memory, which we can't do on the target board. The bare minimum to verify code bytes is repeated here:
1. Set the following levels on these pins:
{| class="wikitable"
|'''Pin'''
|'''Level'''
|-
|RST
|1
|-
|P3.6
|1
|-
|P3.7
|1
|-
|EA/VPP
|1
|-
|ALE/PROG
|1
|-
|PSEN
|0
|-
|P2.6
|0
|-
|P2.7
|1
|-
|}
2. Write the 16 bit address to the following pins:
{| class="wikitable"
|'''Pin'''
|'''Address'''
|-
|P1.0-P1.7
|A0-A7
|-
|P2.0-P2.5
|A8-A13
|-
|P3.4
|A14
|-
|P3.5
|A15
|}
Note that the 87C51 that we've used for this project only has 16 KB of memory, so addresses over 0x3FFF are meaningless (ie: A14 and A15 have no purpose).
3. Write P2.7 to 0 to begin the read. Wait at least 48 clock cycles.
4. Read the 8 bits of data from P0.0-P0.7. These pins use open drain outputs, so pull-up resistors are needed - the AVR's internal pullups are good enough for this.
5. Write P2.7 to 1 to stop reading the device.
== Security ==
== Gotchas ==
