Rabbit 3000, Руководство пользователя

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User’s Manual 115
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.
Note that Parallel Ports D–G behave in the same manner when used as digital I/O.