Serial Module
MOTOROLA
MC68307 USER’S MANUAL
8-23
8.4.1.5 COMMAND REGISTER (UCR). The UCR is used to supply commands to the
UART. Multiple commands can be specified in a single write to the UCR if the commands
are not conflicting—e.g., reset transmitter and enable transmitter commands cannot be
specified in a single command.
MISC3–MISC0—Miscellaneous Commands
These bits select a single command as listed in
Table 8-8.Reset Mode Register Pointer—The reset mode register pointer command causes the
mode register pointer to point to UMR1.
Reset Receiver—The reset receiver command resets the receiver. The receiver is imme-
diately disabled, the FFULL and RxRDY bits in the USR are cleared, and the receiver
FIFO pointer is reinitialized. All other registers are unaltered. This command should be
used in lieu of the receiver disable command whenever the receiver configuration is
changed because it places the receiver in a known state.
Reset Transmitter—The reset transmitter command resets the transmitter. The transmit-
ter is immediately disabled, and the TxEMP and TxRDY bits in the USR are cleared. All
other registers are unaltered. This command should be used in lieu of the transmitter dis-
able command whenever the transmitter configuration is changed because it places the
transmitter in a known state.
Reset Error Status—The reset error status command clears the RB, FE, PE, and OE bits
(in the USR). This command is also used in the block mode to clear all error bits after a
data block is received.
Reset Break-Change Interrupt—The reset break-change interrupt command clears the
delta break (DBx) bits in the UISR.
Start Break—The start break command forces TxD low. If the transmitter is empty, the
start of the break conditions can be delayed up to one bit time. If the transmitter is active,
UCR
MBASE + $105
7
6
5
4
3
2
1
0
—
MISC2
MISC1
MISC0
TC1
TC0
RC1
RC0
RESET:
0
Write Only
Supervisor or User
Table 8-8. MISCx Control Bits
MISC2
MISC1
MISC0
Command
0
No Command
0
1
Reset Mode Register Pointer
0
1
0
Reset Receiver
0
1
Reset Transmitter
1
0
Reset Error Status
1
0
1
Reset Break-Change Interrupt
1
0
Start Break
1
Stop Break