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I/O trouble

Hello guys,

I am having trouble with writing into an 8 bit register which has a RD, WR and CS associated with it from a PIC18f452. The device I'm trying to write to is called an Anybus-s device and I should mention that I am a newbie to the world of micro-controllers.

I've tried 2 methods; 1st. I used the PSP device of the PIC, where the

8bits of portD is directly connected to the 8bits of my device. The WR, RD and CS of the PIC connect to the RD, WR and CS of the device in the order I've written. To read from the device I make WR and CS of the PIC go low and read whts in PORTD (e.g. temp = PORTD).This works alright however, when I want to write by making the RD and CS of the PIC go low and PORTD = BINARYVALUE nothing happens.

2nd method. I don't use the PSP device but I still connect PORTD to the

8bit register and have RE0 connected to RD, RE1 to WR and RE2 connected to CS of the device. When I want to read of the device I make PORTD inputs and set RE0 and RE2 low (then high again), then temp = PORTD to read. This also works fine, however when I want to write by making RE1 an RE2 low, PORTD outputs and PORTD = BINARYVALUE nothing happens again.

The way I know the write isn't working is if the data was written properly the device would send a response. When I write to the device I keep the WR and CS low for approximately 40 micro seconds. I can't seem to get the BINARYVALUE (which is e.g 11101100) to appear on the PORTD pins for some reason. If anyone has any suggestions I would be very grateful. For those who might be interested the ANYbus device is used to interface a micro-controller to the PLC so as to have something like a motor controlled by the PLC.

Reply to
aerona
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To use the PSP, _you_ do not control the PORTE bits. The hardware does this for you. If you access the PORTE bits (which you are doing in both cases), you disable PSP. You need to set the low three bits in the PORTE TRIS register to '1' (input mode), and set bit 4 of the PORTE TRIS register to '1' as well (PSPMODE). This enables PSP mode. Once done, do not perform any I/O on the PORT E lines yourself. Then if you input/output to PORTD, the hardware will automatically control the lines for you. The I/O cycle takes two machine instruction times (8 clock cycles) to complete. Because you are controlling the PORT E lines, you are overriding the PSP mode.

Best Wishes

Reply to
Roger Hamlett

And check your PIC data sheet for the timing. Usually the memory master's WR line is connected to the WR line of the peripheral, and RD to RD. If you have an oscilloscope to measure what's actually going on and compare it to what you see on the bus that may be useful.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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Reply to
Tim Wescott

As it turns out the RD of the PIC should connect to the WR of the device since they're both slaves. And the WR of the PIC should connect to the RD of the Device for the same reason. I believe in the case where there is a master and slave WR should connect to WR (or at least we expect that).

Thank you for that....

Reply to
aerona

Thank you for your reply... I should have explained that the way I control the PSP control bits are through external pins connected to them.. Meaning I've made the RD, WR and CS all digital inputs as the datasheet mentions and have 3 pins of PORTA connected to them so as to control them externally... I did this because making them outputs didn't work... both the PIC and the device I'm using are slave devices so I decided to make the PIC the master by having these 3 external control bits

Reply to
aerona

Thank you for your reply.... I should have explained that the way I control the PSP control bits are through external pins connected to them.. Meaning I've made the RD, WR and CS all digital inputs as the datasheet mentions and have 3 pins of PORTA connected to them so as to control them externally... I did this because making them outputs didn't work... both the PIC and the device I'm using are slave devices so I decided to make the PIC the master by having these 3 external control bits...

Reply to
aerona

If they're both slaves then they'll both sit there waiting for something to happen, and it never will.

Your best bet would probably be to study the datasheet carefully and just bit-bang the control lines from the PIC.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/
Reply to
Tim Wescott

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