Jameco Electronics 2000 • Parallel Inputs, • Full Functionality, • Parallel Outputs, • Slave Port

The functionality of the Parallel Port F pins is not affected for pulse width modulation out- puts and serial clock outputs, except that the Parallel Port F function and direction regis- ters should be set up before a conflicting function on Parallel Port A is in use, since writing to these registers also writes to the Parallel Port A output register.

9.6.1.1 Summary

Parallel Port A	Parallel Port F
• Parallel Inputs	• Full Functionality
• Parallel Outputs	• Parallel Inputs, PWM, Serial Port Clocks
• Slave Port	• Parallel Inputs, PWM, Serial Port Clocks
• Auxiliary I/O Bus	• Full Functionality

•If you enable the auxiliary I/O bus, which uses Parallel Port A, then the bug does not manifest itself and you can use the full functionality of Parallel Port F.

•If you use Parallel Port A as inputs, then the bug does not manifest itself and the full functionality of Parallel Port F is available.

•If you use Parallel Port A as outputs, then you cannot use Parallel Port F pins as outputs too, except that you can use the PWM and clock outputs provided that you are aware that writing to the control registers of Parallel Port F will also write to the data output register of Parallel Port A. A simple way to resolve this is to leave Parallel Port A as an input until you complete the setup of Parallel Port F and then switch Parallel Port A to be an output. You can always use pins on Parallel Port F as inputs.

•If you enable the slave port, then you cannot use Parallel Port F as parallel outputs, but you can still use the other output functions of Parallel Port F following the precautions regarding setup described above.

The easiest approach to avoid any problem when there is a conflict is to assign inputs and outputs in such a manner as to avoid the bug. Either Parallel Port A can be used as inputs, in which case Parallel Port F has full function, or if Parallel Port A cannot be used as inputs, use any pins on Parallel Port F not used for PWM or serial clock outputs as inputs and take the precaution of setting up Parallel Port F before the conflicting functionality of Parallel Port A is enabled.

142 Rabbit 3000 Microprocessor