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sean
Joined: 14 Jul 2004 Posts: 3
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PORT_A_PULLUPS() function |
Posted: Mon Sep 06, 2004 9:40 am |
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I am using PCWM compiler version 3.205, PIC 16F876A chip at 20 MHz.
The Compiler documentation from CCS on page 125, indicates that PORT_A_PULLUPS() function is available for 14 bit PCM devices. But, compiler generates an error - "Undefined identifier port_a_pullups". This function for port_b works wihout any error. In other words, I can use PORT_B_PULLUPS(TRUE) without any compiler errors.
Docimentaion about the microcontroller from Microchip states that PORTB can be software programmed for internal weak pull-ups on all inputs. There is no such statement for PORTA. Therefore, I am suspecting that weak pull-ups are not available on PORTA of 16F876A chip. Can somebody please confirm?
2. If this is correct, then how can I simulate weak pull-ups on portA? I need to read the PortA pins low, if they are pulled low externally but they should be read high if no signal is applied.
Thanks in advance
Sean |
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Ttelmah Guest
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Re: PORT_A_PULLUPS() function |
Posted: Mon Sep 06, 2004 10:03 am |
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sean wrote: | I am using PCWM compiler version 3.205, PIC 16F876A chip at 20 MHz.
The Compiler documentation from CCS on page 125, indicates that PORT_A_PULLUPS() function is available for 14 bit PCM devices. But, compiler generates an error - "Undefined identifier port_a_pullups". This function for port_b works wihout any error. In other words, I can use PORT_B_PULLUPS(TRUE) without any compiler errors.
Docimentaion about the microcontroller from Microchip states that PORTB can be software programmed for internal weak pull-ups on all inputs. There is no such statement for PORTA. Therefore, I am suspecting that weak pull-ups are not available on PORTA of 16F876A chip. Can somebody please confirm?
2. If this is correct, then how can I simulate weak pull-ups on portA? I need to read the PortA pins low, if they are pulled low externally but they should be read high if no signal is applied.
Thanks in advance
Sean |
It's called resistors...
The point about the CCS comment, is that some of the 14bit devices, support pull-ups on PortA, and the CCS code now supports this. However it can't make a hardware feature exist where it is not present. Generally chips that have a PortB, do not support this feature. If you need your lins to float high, the answer is to add a small resistor pack to give this feature.
Best Wishes |
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drh
Joined: 12 Jul 2004 Posts: 192 Location: Hemet, California USA
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Posted: Mon Sep 06, 2004 10:07 am |
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You will have to connect a "pullup" resistor at each porta pin that you need to "read". _________________ David |
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