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Eprom 16x16 Map tracer - advice needed

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Junior Member level 2
Apr 29, 2002
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16x16 map

This is an automotive related topic. Basicaly i have the following citcuit up and running. but for some strange reason, when its accessing the upper regions (colum 13,14,15,16) of the 16x16 matrix its having issues.. could be a circuit problem or an atmel micro issue.

The outputs from the 374 latch goto a port on an atmel processor, which constantly reads in the port, and sends it via serial.. where my software catches the bit stream, finds the start bit and displays where it is on a 16x16 matrix.. Very simple VB coding..

Can anyone outline any issues i may be encountering here? any chip selections i should make? HCT or HC series etc?

*200ns OE -> data output valid eprom times
*Map locations only read twice per rpm. motors reving to ~ 7,500rpm
*Atmel Serial BAUD rate @ 19,200

The 4-16 and 3-8 line decoders are used to select which region to look in for a given 256bit address range(16x16 matrix)... only ever one switch on each dil bank is selected at one time for one output from the 138 and 154..

Would it be wise to take the output from the AND gate and use this as an external interupt on an Atmel 8L?

The maximum access' to the 16x16 selected matrix would be 250times/second. ~ 4ms? a 16MHz micro would be able to be interupt'd, read in port, do some command and upload this via 19,200 baud serial yes?

4ms = 64,000 cycles?

My uplink stream is 4 bytes, 32bit. thats 600 packets max a second @ 19,200..

Read Port A
Compare to last Read, if different continue
Encode into packet
Upload to serial
End Interupt

or am i way off the pase?[/code]

I'm having issues with this circuit.. i dont know why it isn't working! the data coming out doesn't look correct at all..

could the lack of capasitors be a problem here?

ahhhhh classic PEBKAC :) had a hc00 instead of a hc08 in the circuit.. just put an hc04 as a quick fix :)

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