
XBUS asynchronous / synchronous serial interface
UM0404
DocID13284 Rev 2
Figure 106. Asynchronous mode of serial channel XASC
Asynchronous data frames
8-bit data frames
either consist of 8 data bits D7...D0 (S1M = ‘001b’), or of 7 data bits
D6...D0 plus an automatically generated parity bit (S1M = ‘011b’). Parity may be odd or
even, depending on bit S1ODD in register XS1CON. An even parity bit will be set, if the
modulo-2-sum of the 7 data bits is ‘1’. An odd parity bit will be cleared in this case. Parity
checking is enabled via bit S1PEN (always OFF in 8-bit data mode). The parity error flag
S1PE will be set along with the error interrupt request flag, if a wrong parity bit is received.
The parity bit itself will be stored in bit XS1RBUF.7.
Figure 107. Asynchronous 8-bit data frames
2
CPU
Clock
S1R
Baud Rate Timer
Reload Register
16
Clock
Serial Port Control
Shift Clock
S1M S1STP
S1FE
S1OE
S1PE
S1REN
S1FEN
S1PEN
S1OEN
S1LB
Receive Interrupt
Request
Transmit Interrupt
Request
Error Interrupt
Request
Transmit Shift
Register
Receive Shift
Register
TXD1 Output
Transmit Buffer
Register XS1TBUF
Receive Buffer
Register XS1RBUF
Sampling
MUX
0
1
RXD1 Input
Internal X-Bus
P8.7
P8.6
2nd
Stop
bit
Start
bit
D0
(LSB)
D1
D2
D3
D4
D5
D6
D7 /
Parity
(1st)
Stop
Bit