Using Port A as a general purpose output - MC9S12C32 controller

[KH_SRNL]

This should be really simple, but I'm stuck.  I want to use a bit on Port A to drive a chip select line on a peripheral chip.  The problem is I don't appear to be toggling the Port A pin.  My test code snippet is very simple:

DDRA = 0xff;

while(1)

{

PTAD = 0x00;

delay(5000);

PTAD = 0xff;

delay(5000);

}

I verified the routine with Port T and it works fine.  I'm looking at the output of Port A with a meter and seeing no state change.  I'm assuming that Port A can drive the line high (without a pull-up resistor).  The chip is on an ElMicro CHIPS12 carrier board and I'm using the Imagecraft V6 compiler.  Any ideas on what's going on???

Message Edited by KH@SRNL on 2008-05-28 09:04 PM

[KH_SRNL]

Thanks, but that's not quite it.  I caught my own mistake (eventually).

DDRAD is the correct port configuration register (I was using DDRA).  DDRAD sets the port pins as input or output.

PTAD is the general purpose digital input / output port

PORTA is the digital input only read register

[kef]

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KH@SRNL wrote:

PORTA is the digital input only read register

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No, PORTA is port A I/O R/W data register.

PTAD (I/O) and PORTAD (I-only) are port AD (ATD pins) data registers.

[Lundin]

On HCS12, ports A, B, E and K are called PORTA, PORTB etc. The rest of the ports are called PTT, PTM etc. Very inconsistent.

PORTA is indeed the I/O register.

PORTAD0 is the input-only register from the AD.

PTAD is the name for port A on a HCS08 device.

[kef]

We are talking about C32. And C32 has two AD port data registers, PTAD and PORTAD (according to C32 datasheet there's no PORTAD0 register). PTAD data register belongs to PIM module and read only PORTAD - to ATD module.

[Lundin]

You are correct. I checked the register names by looking at some code I wrote for a C32, but I had forgotten that the code was using the memory map for a DG128...

[allawtterb]

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KH@SRNL wrote:

PTAD is the general purpose digital input / output port

PORTA is the digital input only read register

---

I am not sure when you mean with Port A is a digital input only read register.  Port A can be used as a general purpose I/O but the chip used in your module is the 48 pin package which contains only Bit 0 of Port A.  Your module is using it as the SDA line to connect an I2C EEPROM.

[kef]

DDRA - Port A (PTA) data direction register

PTAD - Port AD (PTAD) data register

PORTA - Port A (PTA) data register

No wonder your code doesn't work.