80C32 Philips Semiconductors, 80C32 Datasheet - Page 17

• Manufacturer Part Number: 80C32
• Description: CMOS single-chip 8-bit microcontrollers
• Manufacturer: Philips Semiconductors

Philips Semiconductors
Table 5.
Baud Rate Generator Mode
Bits TCLK and/or RCLK in T2CON (Table 5) allow the serial port
transmit and receive baud rates to be derived from either Timer 1 or
Timer 2. When TCLK= 0, Timer 1 is used as the serial port transmit
baud rate generator. When TCLK= 1, Timer 2 is used as the serial
port transmit baud rate generator. RCLK has the same effect for the
serial port receive baud rate. With these two bits, the serial port can
have different receive and transmit baud rates – one generated by
Timer 1, the other by Timer 2.
Figure 6 shows the Timer 2 in baud rate generation mode. The baud
rate generation mode is like the auto-reload mode,in that a rollover
in TH2 causes the Timer 2 registers to be reloaded with the 16-bit
value in registers RCAP2H and RCAP2L, which are preset by
software.
1999 Apr 01
80C51 8-bit microcontroller family
8K–64K/256–1K OTP/ROM/ROMless, low voltage (2.7V–5.5V),
low power, high speed (33MHz)
Ba d Rate
Baud Rate
375K
9.6K
2.8K
2.4K
1.2K
OSC
300
110
300
110
T2EX Pin
T2 Pin
Timer 2 Generated Commonly Used
Baud Rates
2
Osc Freq
Osc Freq
12MHz
12MHz
12MHz
12MHz
12MHz
12MHz
12MHz
6MHz
6MHz
Transition
Detector
NOTE: OSC. Freq. is divided by 2, not 12.
C/T2 = 0
C/T2 = 1
Note availability of additional external interrupt.
RCAP2H
FF
FF
FF
FF
FE
FB
FD
F2
F9
EXEN2
Control
Figure 6. Timer 2 in Baud Rate Generator Mode
Timer 2
TR2
Control
RCAP2L
EXF2
FF
D9
B2
C8
1E
AF
8F
64
57
RCAP2L
(8-bits)
Interrupt
17
Timer 2
TL2
The baud rates in modes 1 and 3 are determined by Timer 2’s
overflow rate given below:
The timer can be configured for either “timer” or “counter” operation.
In many applications, it is configured for “timer” operation (C/T2*=0).
Timer operation is different for Timer 2 when it is being used as a
baud rate generator.
Usually, as a timer it would increment every machine cycle (i.e., 1/12
the oscillator frequency). As a baud rate generator, it increments
every state time (i.e., 1/2 the oscillator frequency). Thus the baud
rate formula is as follows:
Where: (RCAP2H, RCAP2L)= The content of RCAP2H and
RCAP2L taken as a 16-bit unsigned integer.
The Timer 2 as a baud rate generator mode shown in Figure 6, is
valid only if RCLK and/or TCLK = 1 in T2CON register. Note that a
rollover in TH2 does not set TF2, and will not generate an interrupt.
Thus, the Timer 2 interrupt does not have to be disabled when
Timer 2 is in the baud rate generator mode. Also if the EXEN2
(T2 external enable flag) is set, a 1-to-0 transition in T2EX
(Timer/counter 2 trigger input) will set EXF2 (T2 external flag) but
will not cause a reload from (RCAP2H, RCAP2L) to (TH2,TL2).
Therefore when Timer 2 is in use as a baud rate generator, T2EX
can be used as an additional external interrupt, if needed.
Modes 1 and 3 Baud Rates + Timer 2 Overflow Rate
Modes 1 and 3 Baud Rates =
(8-bits)
RCAP2H
TH2
Reload
8XC51RA+/RB+/RC+/RD+/80C51RA+
[32
[65536 * (RCAP2H, RCAP2L)]]
Oscillator Frequency
“1”
“1”
8XC51FA/FB/FC/80C51FA
2
“0”
“0”
“0”
Overflow
Timer 1
8XC52/54/58/80C32
“1”
Product specification
16
16
16
SMOD
RCLK
TCLK
SU00068
RX Clock
TX Clock