MOTOROLA
MC68341 USER’S MANUAL
7- 39
OP0—Output Port 0/RTSA
1 = The OP0/RTSA pin functions as the ready-to-send signal for channel A. The
signal is asserted and negated according to the configuration programmed by
RxRTS bit 7 in the MR1A for the receiver and TxRTS bit 5 in the MR2A for the
transmitter.
0 = The OP0/RTSA pin functions as a dedicated output. The signal reflects the
complement of the value of bit 0 of the OP.
7.4.1.15 RECEIVER BUFFER (RB). The RB contains three receiver holding registers and
a serial shift register. The channel's RxDx pin is connected to the serial shift register. The
holding registers act as a FIFO. The CPU32 reads from the top of the stack while the
receiver shifts and updates from the bottom of the stack when the shift register has been
filled (see Figure 7-4). This register can only be read when the serial module is enabled
(i.e., the STP bit in the MCR is cleared).
RBA, RBB
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76543210
RB7
RB6
RB5
RB4
RB3
RB2
RB1
RB0
RESET:
00000000
Read Only
Supervisor/User
RB7–RB0—These bits contain the character in the RB.
7.4.1.16 STATUS REGISTER (SR). The SR indicates the status of the characters in the
FIFO and the status of the channel transmitter and receiver. This register can only be read
when the serial module is enabled (i.e., the STP bit in the MCR is cleared).
SRA, SRB
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76543210
RB
FE
PE
OE
TxEMP
TxRDY
FFULL
RxRDY
RESET:
00000000
Read Only
Supervisor/User
RB—Received Break
1 = An all-zero character of the programmed length has been received without a stop
bit. The RB bit is only valid when the RxRDY bit is set. Only a single FIFO
position is occupied when a break is received. Further entries to the FIFO are
inhibited until the channel RxDx returns to the high state for at least one-half bit
time, which is equal to two successive edges of the internal or external 1
× clock
or 16 successive edges of the external 16
× clock.
The received break circuit detects breaks that originate in the middle of a
received character. However, if a break begins in the middle of a character, it
must persist until the end of the next detected character time.
0 = No break has been received.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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