User`s manual

User’s Manual 25
4.1.1 Dedicated Inputs
PB0 is a general CMOS input when the Rabbit 2000 is either not using Serial Port B or is
using Serial Port B in an asynchronous mode. Four other general CMOS input-only pins
are located on PB2–PB5. These pins can also be used for the slave port in master/slave
communication between two processors. PB2 and PB3 are slave write and slave read
strobes, while PB4 and PB5 serve as slave address lines SA0 and SA1, and are used to
access the slave registers.
PC1, PC3, and PC7 are general CMOS inputs only. These pins
can instead be selectively enabled to serve as the serial data inputs for Serial Ports D, C,
and A.
SMODE0 and SMODE1 are read at start-up, and set the mode whereby instructions are
fetched. Thereafter the user may use and read these pins as inputs by reading the Slave
Port Control Register.
NOTE: Exercise care so that the SMODE0 and SMODE1 pins revert to the correct
startup code when a reset occurs.
4.1.2 Dedicated Outputs
One of the general CMOS output-only pins is located on PB7. PB7 can also be used with
the slave port as the /SLAVEATTN output. This configuration signifies that the slave is
requesting attention from the master. PC0, PC2, and PC6 are also output-only pins; alter-
natively, they can serve as the serial data outputs for Serial Ports D, C, and A.
The STATUS pin goes low by default after the first op-code fetch of an instruction cycle.
The STATUS pin may be programmed as a separate output by changing the Rabbit 2000’s
Global Output Control Register.
4.1.3 Memory I/O Interface
Four of the Rabbit 2000 address lines (A0–A3) and all the data lines (D0–D7) are avail-
able. I/0 write (/IOWR) and I/0 read (/IORD) are also available for interfacing to external
devices.
4.1.4 Other Inputs and Outputs
As shown in Table 1, pins PA0–PA7 can be used to allow the Rabbit 2000 to be a slave to
another processor. The slave port also uses PB2–PB5, PB7, and PE7.
PE0, PE1, PE4, and PE5 can be used for up to two external interrupts. PB0 can be used to
access the clock on Serial Port B of the Rabbit microprocessor. PD4 can be programmed
to be a serial output for Serial Port B. PD5 can be used as a serial input by Serial Port B.