Maxim Integrated 71M6521BE Energy Meter IC Family Software - Manual (Page 123)

71M652X Software User’s Guide
Revision 1.7 TERIDIAN Proprietary 123 of 138
© Copyright 2005-2007 TERIDIAN Semiconductor Corporation
Mode 1
Pin rxd0 serves as an input, and txd0 serves as a serial output. No external shift clock is used. 10 bits are transmitted:
a start bit (always 0), 8 data bits (LSB first), and a stop bit (always 1). On receive, a start bit synchronizes the
transmission. 8 data bits are available by reading S0BUF, and the stop bit sets the flag RB80 in the Special Function
Register S0CON. In mode 1 either the internal baud rate generator or timer 1 can be use to specify the baud rate.
Mode 2
This mode is similar to Mode 1, with two differences. The baud rate is fixed at 1/32 or 1/64 of the oscillator frequency
and 11 bits are transmitted or received: a start bit (0), 8 data bits (LSB first), a programmable 9
th bit, and a stop bit (1).
The 9 th bit can be used to control the parity of the serial interface: at transmission, bit TB80 in S0CON is output as the
9 th bit, and at receive, the 9 th bit affects RB80 in the Special Function Register S0CON.
Mode 3
The only difference between Mode 2 and Mode 3 is that in Mode 3, either the internal baud rate generator or timer 1
can be use to specify the baud rate.
Note: The common FLAG protocol requires the data format to be 7E1. This can be implemented using one of the 8-bit
modes, where the MSB (bit 0) is the parity bit. In this mode, the MPU calculates parity
Serial Interface 0 Control Register (S0CON).
The function of the serial port 0 depends on the setting of the Serial Port Control Register S0CON.
MSB LSB
SM0 SM1 SM20 REN0 TB80 RB80 TI0 RI0
Table 6-27: The S0CON Register
Bit Symbol Function
S0CON.7 SM0 Sets baud rate
S0CON.6 SM1 Sets baud rate
S0CON.5 SM20 reserved
S0CON.4 REN0 If set, enables serial reception. Cleared by software to disable reception.
S0CON.3 TB80 The 9 th transmitted data bit in Modes 2 and 3. Set or cleared by the MPU,
depending on the function it performs (parity check, multiprocessor
communication etc.)
S0CON.2 RB80 In Modes 2 and 3 it is the 9 th data bit received. In Mode 1, if SM20 is 0,
RB80 is the stop bit. In Mode 0 this bit is not used. Must be cleared by
software
S0CON.1 TI0 Transmit interrupt flag, set by hardware after completion of a serial
transfer. Must be cleared by software.
S0CON.0 RI0 Receive interrupt flag, set by hardware after completion of a serial
reception. Must be cleared by software
Table 6-28: The S0CON Bit Functions