LED and Switch EXAMPLE not working fully

[christoph]

Hi team,

Using Matrix Multimedia's: 'Reading a switch and outputing to a LED' example with a PIC16F88 on an HP488-00-3 Development board and the switches on Port A / LED's on Port B, I am only able to switch on LED's 0 to 4 on the board after programming the chip succesfully. LED's 5,6 and 7 don't light. The flowchart simulation works fine for all LED's. I have tried playing about with everything I can think of via Flowcode, PPPv3, the board and configuration settings + another two 16F88's but all to no avail .

Desperately need some direction on this 'cos I was really just testing the chip before I used it on my project breadboard!!

Thanks in anticipation,

Chris

[Steve]

Hi Chris,

On the 16F88 (and most other PICmicros) pin A5 is multiplexed with the MCLR function and A6/A7 are multiplexed with the oscillator connections.

On the HP488, these pins are hardwired to the reset and oscillator circuits and do not go to the i/o lines. The circuit diagram for the HP488 should be ont he last page of the datasheet (which can be found in our Learning Centre).

A similar issue exists on our EB006 board, but on this the A6/7 pins can be used as i/o if the chip is set to use an internal oscillator and the appropriate jumper on the board is in the A6&A7 position.

I hope this clears up any confusion.

[christoph]

Hi Steve,

I see what you mean. I am ultimately using the F88 as a uart transmitter for as many switch inputs as I am able to use. I know that Pin 11 (TX output) - naturally - will be unavailable butif I use the internal oscillator and no reset would I be able to use A5, A6 and A7 ???

Chris

[Steve]

I believe so, but you should check the electrical characteristics of these pins in the device datasheet (for example, one of them might be input only).

Also note that the internal oscillator is not as accurate as an external crystal oscillator and is more prone to variations due to temperature, etc. This may affect the UART comms.

[christoph]

THANKYOU Steve!