Jameco Electronics Rabbit 3000 - Manual (Page 151)

142 Rabbit 3000 Microprocessor
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
• 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.
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