Freescale Semiconductor, Inc.
7.4.1.17 MODE REGISTER 2 (MR2). MR2 controls some of the serial module
configuration. This register can be read or written at any time the serial module is enabled
(i.e., the STP bit in the MCR is cleared).
MR2A, MR2B
$720, $721
7
6
5
4
3
2
1
0
CM1
CM0
TxRTS TxCTS
SB3
SB2
SB1
SB0
RESET:
0
0
0
0
0
0
0
0
Read/Write
Supervisor/User
CM1–CM0—Channel Mode
These bits select a channel mode as listed in Table 7-9. See 7.3.3 Looping Modes for
more information on the individual modes.
Table 7-9. CMx Control Bits
CM1
CM0
Mode
0
0
1
1
0
1
0
1
Normal
Automatic Echo
Local Loopback
Remote Loopback
TxRTS—Transmitter Ready-to-Send
This bit controls the negation of the RTSA or RTSB signals. The output is normally
asserted by setting OP0 or OP1 and negated by clearing OP0 or OP1 (see 7.4.1.15
Output Port Control Register (OPCR)).
1 = In applications where the transmitter is disabled after transmission is complete,
setting this bit causes the particular OP bit to be cleared automatically one bit
time after the characters, if any, in the channel transmit shift register and the
transmitter holding register are completely transmitted, including the programmed
number of stop bits. This feature is used to automatically terminate transmission
of a message. If both the receiver and the transmitter in the same channel are
programmed for RTS control, RTS control is disabled for both since this is an
incorrect configuration.
0 = Clearing this bit has no effect on the transmitter RTS≈.
7- 38
MC68340 USER’S MANUAL
MOTOROLA
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