Jameco Electronics 3000, 2000 manual stop bit 7

Figure 12-9illustrates the standard asynchronous serial output patterns.

0

stop bit

7

start bit		data bits		9th bit low
	Character with 9th bit low					stop bit
	0		7
start bit Character w/o 9th bit low							stop bit
	0		7
start bit	Character w. 9th bit high
					9th bit high

Generated by a Write to SxLR

Signal shown at output pin on processor. A “1” is high.

Figure 12-9. Asynchronous Serial Output Patterns

12.9.6 Parity, Extra Stop Bits with 7-Data-Bit Characters

If only 7 data bits are being sent, sending an additional parity or signal bit is easily solved by sending 8 bits and always setting bit 7 (the eighth bit) of the byte to "1" or “0” depend- ing on what is desired. No special precautions are needed if two stop bits are to be received. If parity is received with 7 data bits, receive the data as 8 bits, and the parity will be in the high bit of the byte.

12.9.7 Parity, Extra Stop Bits with 8-Data-Bit Characters

In order to receive parity with 8 data bits, a check is made on each character for a 9th bit low. The 9th bit, or parity bit, is low if bit 6 of the serial port status register (SxSR) is set to a "1" after the character is received. If the 9th bit is not a zero, then the serial port treats it as an extra stop bit. So if the 9th bit low flag is not set, it should be assumed that the parity bit is a "1."

Setting the 9th bit high or low can easily be done in the Rabbit 3000. The 9th bit can be set low by a write to the Serial Port A-F Address Register (SxAR) and the 9th bit can be set high by a write to the Serial Port A-F Long Stop Register (SxLR).

User’s Manual 195