Rabbit RabbitCore RCM4400W Product Manual - page 43

OEM User’s Manual

35

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 RCM4400W 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 communication), 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\RCM4400W\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