Jake

This may be a stupid question but are you waiting 10mS (check data sheet for
exact time) for the PIC to complete the erase-program cycle before reading
back ? (BTW program only is faster)

Robin Abbott - robin.abbott@fored.co.uk

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----- Original Message -----
From: Jake Szot <piclist@HOME.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: 28 November 1999 21:10
Subject: 16f877 parallel programer problem


> Help!
>
> A classmate and I are making a PIC16f877 programmer as a project in one
> of our courses and we've run into a problem. The PIC will not let us
> read data (properly) or advance the program counter while in program
> mode. Here are the steps we go through to program a location:
>
> 0. Issue a Bulk Erase Programing Memory
> 1. Reset the PIC by keeping RB6 and RB7 low and then bringing MCLR from
> 0v to 12.5v
> 2. Issue a Load Data for Program Memory command (6 clks) followed by
> clocking in the data (16 clks)
> 3. Issue a Begin Erase Programming Cycle command (6 clks)
> 4. Issue a Read Data From Program Memory (6 clks) to see if the data
> went in properly
> 5. Change our Data Out to High Impedance
> 6. Issue 16 clks to read the data from the PIC
>
> What comes out from the PIC (during these 16 clocks) is not what we
> programmed. It is all 1's.
>
> Now, if we perform a reset (ie step 1) and issue another Read Data From
> Program Memory (ie steps 4 through 6) we receive the correct data that
> we entered in!
>
> Further more, if we try to program the first two memory locations ie:
>
> 1. Reset the chip
> 2. Issue a Load Data For Program Memory
> 3. Issue a Begin Erase Programing Cycle
> 3. Clock in some data
> 4. Issue an Increment Address
> 5. Issue a Load Data For Program Memory
> 6. Issue a Begin Erase Programing Cycle
>
> Then reset the chip. We can read back the first location ok however the
> second location does not give us our data. Again it is all 1's.
>
> Any help would be greatly appreciated. Please try to respond to
> jakeszot@home.com as I don't know if I will be able to monitor this
> list for responses.
>
> Thanks!
>
> -Jake