FDS 6531/6532 005
Data Sheet 71M6531D/F-71M6532D/F
WDCON[7] selects whether timer 1 or the internal baud rate generator is used. All UART transfers are
programmable for parity enable, parity, 2 stop bits/1 stop bit and XON/XOFF options for variable commu-
nication baud rates from 300 to 38400 bps. Table 15 shows how the baud rates are calculated. Table 16
shows the selectable UART operation modes.
Table 15: Baud Rate Generation
Using Timer 1
(WDCON[7] = 0)
Using Internal Baud Rate Generator
(WDCON[7] = 1)
2smod * fCKMPU/ (384 * (256-TH1))
2smod * fCKMPU/(64 * (210-S0REL))
UART0
UART1
N/A
fCKMPU/(32 * (210-S1REL))
S0REL and S1REL are 10-bit values derived by combining bits from the respective timer reload registers.
SMOD is the SMOD bit in the SFR PCON register. TH1 is the high byte of timer 1.
Table 16: UART Modes
UART 0
UART 1
Start bit, 8 data bits, parity, stop bit, variable
baud rate (internal baud rate generator)
Mode 0
Mode 1
Mode 2
Mode 3
N/A
Start bit, 8 data bits, stop bit, variable
baud rate (internal baud rate generator
or timer 1)
Start bit, 8 data bits, parity, stop bit,
fixed baud rate 1/32 or 1/64 of fCKMPU
Start bit, 8 data bits, parity, stop bit, va-
riable baud rate (internal baud rate ge-
nerator or timer 1)
Start bit, 8 data bits, stop bit, variable baud
rate (internal baud rate generator)
N/A
N/A
Parity of serial data is available through the P flag of the accumulator. 7-bit serial modes with
parity, such as those used by the FLAG protocol, can be simulated by setting and reading bit 7 of
8-bit output data. 7-bit serial modes without parity can be simulated by setting bit 7 to a constant
1. 8-bit serial modes with parity can be simulated by setting and reading the 9th bit, using the
control bits TB80 (S0CON[3]) and TB81 (S1CON[3]) in the S0CON and S1CON SFRs for transmit
and RB81 (S1CON[2]) for receive operations.
The feature of receiving 9 bits (Mode 3 for UART0, Mode A for UART1) can be used as handshake sig-
nals for inter-processor communication in multi-processor systems. In this case, the slave processors
have bit SM20 (S0CON[5]) for UART0, or SM21 (S1CON[5] for UART1, set to 1. When the master pro-
cessor outputs the slave’s address, it sets the 9th bit to 1, causing a serial port receive interrupt in all the
slaves. The slave processors compare the received byte with their address. If there is a match, the ad-
dressed slave will clear SM20 or SM21 and receive the rest of the message. All other slaves will ignore
the message. After addressing the slave, the host outputs the rest of the message with the 9th bit set to 0,
so no additional serial port receive interrupts will be generated.
UART Control Registers:
The functions of UART0 and UART1 depend on the setting of the Serial Port Control Registers S0CON
and S1CON shown in Table 17 and
Table 18, respectively and the PCON register shown in Table 19.
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