MOTOROLA
MC68341 USER’S MANUAL
7- 35
7.4.1.12 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
76543210
CM1
CM0
TxRTS
TxCTS
SB3
SB2
SB1
SB0
RESET:
00000000
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
Normal
0
1
Automatic Echo
1
0
Local Loopback
1
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 in the OPCR and negated by clearing OP0 or OP1 in
the OPCR (see 7.4.1.14 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≈.
TxCTS—Transmitter Clear-to-Send
1 = Enables clear-to-send operation. The transmitter checks the state of the CTS≈
input each time it is ready to send a character. If CTS≈ is asserted, the character
is transmitted. If CTS≈ is negated, the channel TxDx remains in the high state,
and the transmission is delayed until CTS≈ is asserted. Changes in CTS≈ while a
character is being transmitted do not affect transmission of that character. If both
TxCTS and TxRTS are enabled, TxCTS controls the operation of the transmitter.
0 = The CTS≈ has no effect on the transmitter.
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Freescale Semiconductor, Inc.
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Go to: www.freescale.com
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