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2.1.1 Dedicated Inputs
PB0 and PB1 are designated as inputs because the
Rabbit 2000 is operating in an asynchronous mode.
Four of the input-only pins are located on PB2–PB5.
These pins are used for the slave port. 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 (SD0–
SD7), which is the alternate assignment for parallel
port A. When Port C is used as a parallel port, PC1,
PC3, PC5, and PC7 are inputs only. These pins can
alternately be selectively enabled to serve as the
serial data inputs for Serial Ports D, C, B, and A.
2.1.2 Dedicated Outputs
Two of the output-only pins are located on PB6–
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 mas-
ter. When Port C is used as a parallel port, PC0,
PC2, PC4 and PC6 are outputs only. These pins can
alternately serve as the serial data outputs for Serial
Ports D, C, B, and A.
2.1.3 Memory I/O Interface
Thirteen of the Rabbit 2000 buffered address lines
(A0–A12) and all the buffered data lines (D0–D7)
are available as outputs. I/0 write (/IOWR), I/0 read
(/IORD), buffer enable (/BUFEN), and Watchdog
Output (/WDO) are also available for interfacing to
external devices.
The STATUS output has three different programma-
ble functions:
It can be driven low on the first op code
1.
fetch cycle.
It can be driven low during an interrupt
2.
acknowledge cycle.
It can also serve as a general-purpose out-
3.
put.
2–6
Hardware Reference
The output clock is available on the PCLK pin. The
primary function of PCLK is as a peripheral clock
or a peripheral clock ÷ 2, but PCLK can instead be
used as a digital output. PCLK can also be disabled
by removing R20 if there is a need to reduce radi-
ated emissions. Removing R20 will disable the
PCLK output on pin 3 of header J1. Alternatively,
PCLK can be disabled in software using Dynamic C
version 7.03 or later.
2.1.4 Additional I/0
Two status mode pins, SMODE0 and SMODE1, are
available as inputs. The logic state of these two pins
determines the startup procedure after a reset.
/RES_IN is an external input used to reset the Rab-
bit 2000 microprocessor and the RabbitCore
RCM2100 memory. /RES_OUT is an output from
the reset circuitry that can be used to reset other
peripheral devices.
2.2
Serial Communication
The RabbitCore RCM2100 board does not have an
RS-232 or an RS-485 transceiver directly on the
board. However, an RS-232 or RS-485 interface
may be incorporated on the board the RCM2100 is
mounted on. For example, the Prototyping Board
supports a standard RS-232 transceiver chip.
2.2.1 Serial Ports
There are four serial ports designated as Serial Ports
A, B, C, and D. All four serial ports can operate in
an asynchronous mode up to the baud rate of the
system clock divided by 32. An asynchronous port
can handle 7 or 8 data bits. A 9th bit address
scheme, where an additional bit is sent to mark the
first byte of a message, is also supported. Serial
Ports A and B can be operated alternately in the
clocked serial mode. In this mode, a clock line syn-
chronously clocks the data in or out. Either of the
two communicating devices can supply the clock.
When the Rabbit 2000 provides the clock, the baud
rate can be up to 1/4 of the system clock frequency,
or 5.52 Mbps for a 22.1 MHz clock speed.
RabbitCore RCM2100 Series
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