UPSD3254 STMICROELECTRONICS [STMicroelectronics], UPSD3254 Datasheet - Page 63

• Manufacturer Part Number: UPSD3254
• Description: Flash Programmable System Devices with 8032 Microcontroller Core
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Baud Rates. The baud rate in Mode 0 is fixed:
Mode 0 Baud Rate = f
The baud rate in Mode 2 depends on the value of
Bit SMOD = 0 (which is the value on reset), the
baud rate is 1/64 the oscillator frequency. If SMOD
= 1, the baud rate is 1/32 the oscillator frequency.
Mode 2 Baud Rate = (2
In the uPSD325X devices, the baud rates in
Modes 1 and 3 are determined by the Timer 1
overflow rate.
Using Timer 1 to Generate Baud Rates. When
Timer 1 is used as the baud rate generator, the
baud rates in Modes 1 and 3 are determined by
the Timer 1 overflow rate and the value of SMOD
as follows (see:
Mode 1,3 Baud Rate =
(2
The Timer 1 Interrupt should be disabled in this
application. The Timer itself can be configured for
either “timer” or “counter” operation, and in any of
its 3 running modes. In the most typical applica-
tions, it is configured for “timer” operation, in the
Auto-reload Mode (high nibble of TMOD = 0010B).
In that case the baud rate is given by the formula:
Mode 1,3 Baud Rate =
(2
Table 45. Timer 1-Generated Commonly Used Baud Rates
SMOD
SMOD
Mode 0 Max: 1MHz
Mode 2 Max: 375K
Modes 1, 3: 62.5K
Baud Rate
/ 32) x (Timer 1 overflow rate)
/ 32) x (f
19.2K
137.5
9.6K
4.8K
2.4K
1.2K
110
110
OSC
/ (12 x [256 – (TH1)]))
OSC
SMOD
11.059MHz
11.059MHz
11.059MHz
11.059MHz
11.059MHz
11.059MHz
/ 12
12MHz
12MHz
12MHz
12MHz
6MHz
f
/ 64) x f
OSC
OSC
UPSD3254A, UPSD3254BV, UPSD3253B, UPSD3253BV
SMOD
X
1
1
1
0
0
0
0
0
0
0
One can achieve very low baud rates with Timer 1
by leaving the Timer 1 Interrupt enabled, and con-
figuring the Timer to run as a 16-bit timer (high nib-
ble of TMOD = 0001B), and using the Timer 1
Interrupt to do a 16-bit software reload. Figure 22
lists various commonly used baud rates and how
they can be obtained from Timer 1.
Using Timer/Counter 2 to Generate Baud
Rates. In the uPSD325X devices, Timer 2 select-
ed as the baud rate generator by setting TCLK
and/or RCLK (see Figure 22, page 56 Timer/
Counter 2 Control Register (T2CON)).
Note: The baud rate for transmit and receive can
be simultaneously different. Setting RCLK and/or
TCLK puts Timer into its Baud Rate Generator
Mode.
The RCLK and TCLK Bits in the T2CON register
configure UART 1. The RCLK1 and TCLK1 Bits in
the PCON register configure UART 2.
The Baud Rate Generator Mode is similar to the
Auto-reload Mode, in that a roll over 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.
Now, the baud rates in Modes 1 and 3 are deter-
mined at Timer 2’s overflow rate as follows:
Mode 1,3 Baud Rate = Timer 2 Overflow Rate / 16
C/T
X
X
0
0
0
0
0
0
0
0
0
Timer 1
Mode
X
X
2
2
2
2
2
2
2
1
2
Reload Value
FEEBh
FDh
FDh
FFh
FAh
E8h
1Dh
F4h
72h
X
X
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