You don't mention what software stack you are using... Simple MAC, 802.15.4MAC, or ZigBee BeeStack.
If you are using ZigBee BeeStack use this:
void Asp_PortReq(uint8_t portWrite, uint8_t *portValue);
If not, you need to write the values directly to the ABEL registers 0x3F. See MC1321xRM (reference manual).
NOTE: Don't foget to set the DDR (Data Direction Register) before hand (during initialization).
If you are using ZigBee BeeStack use this:
void Asp_DdrReq(uint8_t directionMask);
If not, you need to write the values directly to the ABEL registers 0x0B. See MC1321xRM (reference manual).
WARNING: Messing with the radio's GPIO can cause big problems if you are not careful to avoid the I/O used to interface to the main processor. See MC1321xRM (reference manual).
Regards,
- Ware