71M6521BE
Energy Meter IC
DATA SHEET
JANUARY 2008
The 71M6521BE has several UART-related registers for the control and buffering of serial data. All UART transfers are pro-
grammable for parity enable, parity, 2 stop bits/1 stop bit and XON/XOFF options for variable communication baud rates from
300 to 38400 bps. Table 12 shows how the baud rates are calculated. Table 13 shows the selectable UART operation modes.
Using Timer 1
2SMOD * fCKMPU/ (384 * (256-TH1))
N/A
Using Internal Baud Rate Generator
2SMOD * fCKMPU/(64 * (210-S0REL))
UART0
UART1
f
CKMPU/(32 * (210-S1REL))
Note: 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. TH1 is the high byte of timer 1.
Table 12: Baud Rate Generation
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
N/A
Start bit, 8 data bits, stop bit, variable baud
rate (internal baud rate generator or timer 1)
Start bit, 8 data bits, stop bit, variable baud rate
(internal baud rate generator)
Start bit, 8 data bits, parity, stop bit, fixed
baud rate 1/32 or 1/64 of fCKMPU
N/A
Start bit, 8 data bits, parity, stop bit, variable
baud rate (internal baud rate generator or
timer 1)
Mode 3
N/A
Table 13: UART Modes
Parity of serial data is available through the P flag of the accumulator. Seven-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. Seven-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. SM20 (S0CON.5) and SM21 (S1CON.5) can be used as
handshake signals for inter-processor communication in multi-processor systems.
Serial Interface 0 Control Register (S0CON).
The function of the UART0 depends on the setting of the Serial Port Control Register S0CON.
MSB
LSB
SM0
SM1
SM20
REN0
TB80
RB80
TI0
RI0
Table 14: The S0CON Register
Serial Interface 1 Control Register (S1CON).
The function of the serial port depends on the setting of the Serial Port Control Register S1CON.
MSB
LSB
SM
-
SM21
REN1
TB81
RB81
TI1
RI1
Table 15: The S1CON register
V1.0
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