Jameco Electronics Rabbit 3000 - Manual (Page 138)

User’s Manual 129
9. P
ARALLEL
P
ORTS
The Rabbit has seven 8-bit parallel ports designated A, B, C, D, E, F, and G. The pins used
for the parallel ports are also shared with numerous other functions as shown in Table 5-2.
The important properties of the ports are summarized below.
• Port A—Shared with the slave port data interface and auxiliary I/O data bus.
• Port B—Shared with control lines for slave port, auxiliary I/O address bus, and clock
I/O for clocked serial mode option for Serial Ports A and B.
• Port C—Shared with serial port data I/O.
• Port D—4 bits shared with alternate I/O pins for Serial Ports A and B. 4 bits not shared.
Port D can be configured as open drain outputs. Port D also contains output preload
registers that can be clocked into the output registers under timer control for pulse gen-
eration.
• Port E—All bits of Port E can be configured as I/O strobes. 4 bits of port E can be used
as external interrupt inputs. One bit of port E is shared with the slave port chip select.
Port E has output preload registers that can be clocked into the output registers under
timer control for pulse generation.
• Port F— As outputs, Port F can be configured as open drain outputs. Alternatively, Par-
allel Port F outputs can carry the four Pulse-Width Modulator outputs. As inputs, Paral-
lel Port F inputs can carry the inputs to the two channels of the quadrature decoders.
Port F pins can also be configured to be used as clock pins for clocked Serial Ports C
and D.
• Port G—As outputs, Port G can be configured as open drain outputs. Port G inputs and
outputs are also used for access to other serial peripherals on the chip such as those
used for asynchronous or SDLC/HDLC communication.
• Parallel Ports D–G behave in the same manner when used as digital I/O.
NOTE: There may be a conflict in using Parallel Port A and Parallel Port F. Either Paral-
lel 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. Refer to
Section 9.6.1, “Using Parallel Port A and Parallel Port F,” for more information.