668-0003-C Rabbit Semiconductor, 668-0003-C Datasheet - Page 138

• Manufacturer Part Number: 668-0003-C
• Description: IC CPU RABBIT2000 30MHZ 100PQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 668-0003-C

• Rohs Status: RoHS non-compliant
• Processor Type: Rabbit 2000 8-Bit
• Speed: 30MHz
• Voltage: 2.7V, 3V, 3.3V, 5V
• Mounting Type: Surface Mount
• Package / Case: 100-MQFP, 100-PQFP
• Features: -
• Other names: 316-1004; 668-0003

12.7.5 Extra Stop Bits, Sending Parity, 9th Bit Communication Schemes
Some systems may require two stop bits. In some cases, it may be necessary to send a par-
ity bit. Certain systems, such as some 8051-based multidrop communications systems, use
a 9th data bit to mark the start of a message frame. The Rabbit 2000 can receive parity or
message formats that contain a 9th bit without problem. Transmitting messages with par-
ity or messages that always contain a 9th bit is also possible. It is quite easy to do so for
byte formats that use only 7 data bits, in which case the 9th bit or parity bit is actually an
8th bit. Things are a little bit messy for the transmitter software if there are 8 data bits and
a 9th parity or signaling bit is needed. Sending a 9th low bit is supported by hardware.
Sending a 9th bit is easier with revisions A–C of the Rabbit 2000 chip, which have a long
stop register as described in Section B.2.3. Sending a 9th bit in the original Rabbit 2000
chip as a high value required delaying the transmission of the next character by 1 baud,
effectively providing the 9th bit high and a stop bit, which is the same as two stop bits.
Figure 12-8 illustrates the standard asynchronous serial output patterns.
12.7.5.1 Parity, Extra Stop Bits with 7 Data Bit Characters
If only 7 data bits are being sent, the problem of 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” depending 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 par-
ity will be in the high bit of the byte.
132
start bit
start bit
start bit
Character with 9th bit low
Character w/o 9th bit low
Signal shown at output pin on processor. A “1” is high.
0
0
0
Character w. 9th bit high
Figure 12-8. Asynchronous Serial Output Patterns
data bits
7
7
7
9th bit low
9th bit high
stop bit
Rabbit 2000 Microprocessor User’s Manual
stop bit
stop bit
This format is not
sent automatically.