Mitsubishi Motors DS5000TK - Manual (Page 111)

USER’S GUIDE
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value that generates the required time interval at its
overflow. This is the most common mode of communi-
cating with a PC COM port or similar device. When talk-
ing to a PC in Mode 1, the PC would be set to 8–N–1
( 8 bits, no parity, 1 stop). Common baud rates are 2400,
9600, and 19200 bps, but it can communicate as fast as
57,600 bps in Mode 1.
Mode 2 is an 11–bit asynchronous mode using 8 or 9–bit
words and one stop bit. The time base offers a choice of
two fixed relationships of either 32 or 64 oscillator clocks
per bit. It is not otherwise programmable in speed. The
9th bit is selected manually. It can be set to a 1, 0, or par-
ity. Thus Mode 2 could appear to have two stop bits by
selecting the 9th bit to be a logic 1.
Mode 3 is similar to Modes 1 and 2. Like Mode 2, it uses
9–bit words instead of 8. Also like Mode 2, the 9th bit can
be either 0, 1, or parity. Like Mode 1, it uses the Timer 1
mechanism to generate baud rates. This mode can be
used with a PC COM port set for 8–N–2 (8 bits, no parity,
two stop bits) by setting the 9th bit to a 1. It can also sup-
port 8E1 (8 bits, even parity, one stop). Parity is done by
transferring the parity bit (PSW.0) to the 9th bit of the se-
rial port (SCON.3). Since the CPU sets the parity bit to
indicate an odd number of bits in the accumulator, a
9–bit serial word containing this parity bit would have
even parity.
The serial port is controlled by the SCON register at
SFR location 98h. These bits are described below in
Figure 14–1. The serial port begins transmission after
software writes to the SBUF register. Data is always
shifted out with the LSB first. Each mode is discussed in
detail below following Figure 14–1.
SERIAL PORT CONTROL REGISTER Figure 14–1
Bit Description:
SCON.7, SCON.6: SM0, SM1
“Mode Select”: Used to select the operational mode of the serial I/O port as follows:
SM0 SM1 MODE FUNCTION WORD LENGTH
BAUD CLOCK
PERIOD
0 0 Mode 0 Sync 8 bits 12 t
CLK
0 1 Mode 1 Async 10 bits Timer 1 Overflow
1 0 Mode 2 Async 11 bits 64 t
CLK
or 32 t
CLK
1 1 Mode 3 Async 11 bits Timer 1 Overflow
Initialization: Cleared to a 0 on any type of reset.
SCON.5: SM2
“Multiple MCU Comm.”: Used to enable the multiple microcontroller communications feature for
Modes 2 and 3. When SM2=1, RI will be activated only when serial words
are received which cause RB8 to be set to 1.
Initialization: Cleared to a 0 on any type of reset.
SCON.4: REN
“Receive Enable”: When set to 1, the receive shift register will be enabled. Disabled when
cleared to 0.
Initialization: Cleared to a 0 on any type of reset.
SCON.3: TB8
“Xmit Bit 8”: Can be set or cleared to define the state of the 9th data bit in Modes 2 and 3 of
a serial data word.
Initialization: Cleared to a 0 on any type of reset.