Datasheet

71M6541D/F/G and 71M6542F/G Data Sheet
Rev 4
Table 20: The S1CON (UART1) Register (SFR 0x9B)
Bit
Symbol
Function
S1CON[7]
SM
Sets the baud rate and mode for UART1.
SM
Mode
Description
Baud Rate
0
A
9-bit UART
variable
1
B
8-bit UART
variable
S1CON[5]
SM21
Enables the inter-processor communication feature.
S1CON[4]
REN1
If set, enables serial reception. Cleared by software to disable reception.
S1CON[3]
TB81
The 9
th
transmitted data bit in Mode A. Set or cleared by the MPU,
depending on the function it performs (parity check, multiprocessor
communication etc.)
S1CON[2]
RB81
In Modes A and B, it is the 9
th
data bit received. In Mode B, if SM21 is 0,
RB81 is the stop bit. Must be cleared by software
S1CON[1]
TI1
Transmit interrupt flag, set by hardware after completion of a serial transfer.
Must be cleared by software (see Caution above).
S1CON[0]
RI1
Receive interrupt flag, set by hardware after completion of a serial reception.
Must be cleared by software (see Caution above).
Table 21: PCON Register Bit Description (SFR 0x87)
Bit
Symbol
Function
PCON[7]
SMOD
The SMOD bit doubles the baud rate when set
2.4.6 Timers and Counters
The 80515 has two 16-bit timer/counter registers: Timer 0 and Timer 1. These registers can be configured
for counter or timer operations.
In timer mode, the register is incremented every machine cycle, i.e., it counts up once for every 12 periods
of the MPU clock. In counter mode, the register is incremented when the falling edge is observed at the
corresponding input signal T0 or T1 (T0 and T1 are the timer gating inputs derived from certain DIO pins,
see 2.5.8 Digital I/O). Since it takes 2 machine cycles to recognize a 1-to-0 event, the maximum input
count rate is 1/2 of the clock frequency (CKMPU). There are no restrictions on the duty cycle, however
to ensure proper recognition of the 0 or 1 state, an input should be stable for at least 1 machine cycle.
Four operating modes can be selected for Timer 0 and Timer 1, as shown in Table 22 and Table 23. The
TMOD (SFR 0x89) Register, shown in Table 24, is used to select the appropriate mode. The timer/counter
operation is controlled by the TCON (SFR 0x88) Register, which is shown in Table 25. Bits TR1 (TCON[6])
and TR0 (TCON[4]) in the TCON register start their associated timers when set.