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Using port 4 in the P87C51MC2 (extended memory chip from Philips)

Hi,
I'm unable to reset the pin P4.1(TXD1)on target though it's possible on the simulator.
The register setting I'm doing are as follows:

SPCTL = 0x00; //not bit addressable.
TXD1 = 0; // P4 is bit addressable.

I also tried enabling SPCTL.6 and SPCTL.7(this pin tells the SPI logic, not to use the SS-pin (P4.1) and make it available as standard I/O) before writing a '0' to P4.1 but was unsuccessul.

As I said earlier, on the simulator, I can see that port pin is reset while on the target, it is always set.

Why is the behaviour different on the target and simulator for the same code?

Any help would be appreciated.

Warm regards,
Sandy

0 erik malund over 22 years ago

the datashhet says "this port is not available as a general purpose I/O"

Erik
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0 Sundeep Subbarau over 22 years ago in reply to erik malund

No...there is a new data sheet available at http://www.semiconductors.philips.com/acrobat/datasheets/zip/P87C51MB2_MC2-02.zip which states "... Right now, SPI module is available, two more general purpose digital pins on P4 are present ... "

-Sandy
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0 erik malund over 22 years ago in reply to Sundeep Subbarau

page 8 states how to get the problem you see (SPEN). Also, when specs change the changes may only be relevant for the latest revision of the chip.

Erik
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