Jameco Electronics 3000, 2000 manual Parallel Ports

9. PARALLEL PORTS

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.

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