User’s Manual
33
Table 3 summarizes the possible parallel port pins for the serial ports and their clocks.
4.2.1.1 Using the Serial Ports
The receive lines on the RCM4510W serial ports do not have pull-up resistors. If you are using
the serial ports without a receiver chip (for example, for RS-422, RS-232, or RS-485 serial com-
munication), the absence of a pull-up resistor on the receive line will likely lead to line breaks
being generated since line breaks are normally generated whenever the receive line is pulled low.
If you are operating a serial port asynchronously, you can inhibit character assembly during
breaks by setting bit 1 in the corresponding Serial Port Extended Register to 1. Should you need
line breaks, you will have to either add a pull-up resistor on your motherboard or use a receiver
that incorporates the circuits to have the output default to the nonbreak levels.
The Dynamic C
RS232.LIB
library requires you to define the macro
RS232_
NOCHARASSYINBRK
to inhibit break-character assembly for all the serial ports.
#define RS232_NOCHARASSYINBRK
This macro is already defined so that it is the default behavior for the sample programs in the
Dynamic C
SAMPLES\RCM4500W\SERIAL
folder.
Table 3. Rabbit 4000 Serial Port and Clock Pins
Serial Port A
TXA
PC6, PC7, PD6
Serial Port E
TXE
PD6, PE6, PC6
RXA
PC7, PD7, PE7
RXE
PD7, PE7, PC7
SCLKA
PB1
RCLKE
PD5, PE5, PC5
Serial Port B
TXB
PC4, PC5, PD4
TCLKE
PD4, PE4, PC4
RXB
PC5, PD5, PE5
Serial Port F
TXF
PD2, PE2, PC2
SCLKB
PB0
RXF
PD3, PE3, PC3
Serial Port C
TXC
PC2, PC3
RCLKF
PD1, PE1, PC1
RXC
PC3, PD3, PE3
TCLKF
PD0, PE0, PC0
SCLKC
PD2, PE2, PE7, PC7
RCLKE and RCLKF must be selected to be on the
same parallel port as TXE and TXF respectively.
Serial Port D
TXD
PC0, PC1
RXD
PC1, PD1, PE1
SCLKD
PD0, PE0, PE3, PC3
