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Philips Semiconductors
User’s Manual - Preliminary -
P89LPC901/902/903
UART (P89LPC903)
2003 Dec 8 64
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Figure 8-3: Serial Port Control Register (SCON)
SCON
Address: 98h
Bit addressable
Reset Source(s): Any reset
Reset Value: 00000000B
BIT SYMBOL FUNCTION
SCON.7 SM0/FE The use of this bit is determined by SMOD0 in the PCON register. If SMOD0 = 0, this bit
is read and written as SM0, which with SM1, defines the serial port mode. If SMOD0 = 1,
this bit is read and written as FE (Framing Error). FE is set by the receiver when an invalid
stop bit is detected. Once set, this bit cannot be cleared by valid frames but is cleared by
software. (Note: UART mode bits SM0 and SM1 should be programmed when SMOD0 is
’0’ - default mode on any reset.)
SCON. 6 SM1 With SM0, defines the serial port mode (see table below).
SM0, SM1
UART Mode UART 0 Baud Rate
0 0 0: shift register CCLK/16 (default mode on any reset)
0 1 1: 8-bit UART Variable (see Table )
1 0 2: 9-bit UART CCLK/32 or CCLK/16
1 1 3: 9-bit UART Variable (see Table )
SCON.5 SM2 Enables the multiprocessor communication feature in Modes 2 and 3. In Mode 2 or 3, if
SM2 is set to 1, then Rl will not be activated if the received 9th data bit (RB8) is 0. In Mode
0, SM2 should be 0. In Mode 1, SM2 must be 0.
SCON.4 REN Enables serial reception. Set by software to enable reception. Clear by software to disable
reception.
SCON.3 TB8 The 9th data bit that will be transmitted in Modes 2 and 3. Set or clear by software as
desired.
SCON.2 RB8 The 9th data bit that was received in Modes 2 and 3. In Mode 1 (SM2 must be 0), RB8 is
the stop bit that was received. In Mode 0, RB8 is undefined.
SCON.1 TI Transmit interrupt flag. Set by hardware at the end of the 8th bit time in Mode 0, or at the
the stop bit (see description of INTLO bit in SSTAT register) in the other modes. Must be
cleared by software.
SCON.0 RI Receive interrupt flag. Set by hardware at the end of the 8th bit time in Mode 0, or
approximately halfway through the stop bit time in Mode 1. For Mode 2 or Mode 3, if
SMOD0, it is set near the middle of the 9th data bit (bit 8). If SMOD0 = 1, it is set near the
middle of the stop bit (see SM2 - SCON.5 - for exceptions). Must be cleared by software.
76543210
SM0/FE SM1 SM2 REN TB8 RB8 TI RI