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8255 Interfaced to ADC and DAC

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magnetra

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The attached PDF is an extract from datasheet for 8255A PPI chip. I think the example for interfacing 8255 with ADC and DAC has some mistakes.
1> PC4-PC7 have been used twice.
2> PC0-PC3 have been used in BSR mode, but I can't figure out how they help in the interface.

Could anyone explain how the interface actually work?

Regards
M
 

I think there is an error. The input port for the ADC is the PORTB and the used bits are PB0, PB1, PB2, PB3, PB4, PB5, PB6 and PB7. The bit PC0 is used to strobe the data into the DAC, PC1=?. PC2 starts the conversion of the ADC. PC3 is used to enable output data from ADC.
Bye!
 

You don't "talk" to both devices at the same time, so PC4-PC7 with the DAC are used as INPUTS and with 12-bit ADC as OUTPUTS, and PC0-PC1/PC2-PC3 as control bits ..
Bear in mind, in the 8255 PPI, depending on the selected mode, you can address PC port by bits, and it is devided into two halves, where each of them can be defined as inputs or outputs ..

I can't see any errors there ..

Regards,
IanP
 

Thanks IanP. But why would we want to use PC4-PC7 for input from ADC(whose lower nibble is interfaced to port B) while we still have PB4-PB7 left unused?

M
 

You are designer .. you choose pins that suit you ..

This diagram is just an example ..

You are right, more logical is to use the whole port (B in this case) than to mix inputs from different ports ..

Regards,
IanP
 

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