MAXQ612/MAXQ622 User’s Guide
5-20 Maxim Integrated
REGISTER DESCRIPTION
SCON1 (02h, 03h) Serial Port 1 Control Register
Initialization: The serial port control is cleared to 00h on all forms of reset.
Read/Write Access: Unrestricted read/write.
SCON1.0 (RI) Receive Interrupt Flag. This bit indicates that a data byte has been received in the serial
port buffer. The bit is set at the end of the 8th bit for mode 0, after the last sample of the
incoming stop bit for mode 1 subject to the value of the SM2 bit, or after the last sample of
RB8 for modes 2 and 3. This bit must be cleared by software once set.
SCON1.1 (TI) Transmit Interrupt Flag. This bit indicates that the data in the serial port data buffer has
been completely shifted out. It is set at the end of the last data bit for all modes of operation
and must be cleared by software once set.
SCON1.2 (RB8) 9th Received Bit State. This bit identifies the state of the 9th bit of received data in serial
port modes 2 and 3. When SM2 is 0, it is the state of the stop bit in mode 1. This bit has no
meaning in mode 0.
SCON1.3 (TB8) 9th Transmission Bit State. This bit defines the state of the 9th transmission bit in serial
port modes 2 and 3.
SCON1.4 (REN)
Receive Enable
REN_0 = 0: Serial port 0 receiver disabled.
REN_0 = 1: Serial port 0 receiver enabled for modes 1, 2, and 3. Initiate synchronous
reception for mode 0.
SCON1.5 (SM2) Serial Port 1 Mode Bit 2. Setting this bit in mode 1 ignores reception if an invalid stop
bit is detected. Setting this bit in mode 2 or 3 enables multiprocessor communications,
and prevents the RI bit from being set and the interrupt from being asserted if the 9th bit
received is 0. This bit also used to support mode 0 for clock selection:
SM2 = 0: Clock is divided by 12.
SM2 = 1: Clock is divided by 4.
SCON1.6 (SM1)
SCON1.7 (SM0/FE)
Serial Port 1 Mode Bits 1:0 (when FEDE is 0). When FEDE is set to 1, this bit is the Framing
Error Flag that is set upon detection of an invalid stop bit. It must be cleared by software.
Modification of this bit when FEDE is set has no effect on the serial mode.
MODE SM2 SM1 SM0 FUNCTION
LENGTH
(BITS)
PERIOD
0 0 0 0 Synchronous 8 12 system clocks
0 1 0 0 Synchronous 8 4 system clocks
1 x 1 0 Asynchronous 10
64/16 baud clocks
(SMOD = 0/1)
2 0 0 1 Asynchronous 11
64/32 system
clocks (SMOD =
0/1)
2 1 0 1 Asynchronous (MP) 11
64/32 system
clocks (SMOD =
0/1)
3 0 1 1 Asynchronous 11
64/16 baud clocks
(SMOD = 0/1)
3 1 1 1 Asynchronous (MP) 11
64/16 baud clocks
(SMOD = 0/1)
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