UPSD3234AV-24U1T STMicroelectronics, UPSD3234AV-24U1T Datasheet - Page 57

• Manufacturer Part Number: UPSD3234AV-24U1T
• Description: Flash Programmable System Devices with 8032 Microcontroller Core and 64Kbit SRAM
• Manufacturer: STMicroelectronics

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Table 44. Description of the SCON Bits
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 uPSD323X 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
SMOD
SMOD
Bit
7
6
5
4
3
2
1
0
/ 32) x (Timer 1 overflow rate)
/ 32) x (f
Symbol
OSC
SM0
SM1
SM2
REN
RB8
TB8
RI
TI
/ (12 x [256 – (TH1)]))
OSC
SMOD
/ 12
(SM1,SM0)=(0,0): Shift Register. Baud rate = f
(SM1,SM0)=(1,0): 8-bit UART. Baud rate = variable
(SM1,SM0)=(0,1): 8-bit UART. Baud rate = f
(SM1,SM0)=(1,1): 8-bit UART. Baud rate = variable
Enables the multiprocessor communication features in Mode 2 and 3. In Mode 2 or 3, if
SM2 is set to '1,' RI will not be activated if its received 8th data bit (RB8) is '0.' In Mode 1,
if SM2=1, RI will not be activated if a valid Stop Bit was not received. In Mode 0, SM2
should be '0'
Enables serial reception. Set by software to enable reception. Clear by software to
disable reception
The 8th data bit that will be transmitted in Modes 2 and 3. Set or clear by software as
desired
In Modes 2 and 3, this bit contains the 8th data bit that was received. In Mode 1, if
SM2=0, RB8 is the Snap Bit that was received. In Mode 0, RB8 is not used
Transmit Interrupt Flag. Set by hardware at the end of the 8th bit time in Mode 0, or at
the beginning of the Stop Bit in the other modes, in any serial transmission. Must be
cleared by software
Receive Interrupt Flag. Set by hardware at the end of the 8th bit time in Mode 0, or
halfway through the Stop Bit in the other modes, in any serial reception (except for
SM2). Must be cleared by software
/ 64) x f
OSC
uPSD3234A, uPSD3234BV, uPSD3233B, uPSD3233BV
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.
22., page 51
rates and how they can be obtained from Timer 1.
Using Timer/Counter 2 to Generate Baud
Rates. In the uPSD323X Devices, Timer 2 select-
ed as the baud rate generator by setting TCLK
and/or RCLK (see
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
Function
OSC
OSC
lists various commonly used baud
/64 or f
/12
OSC
Figure 22., page 51
/32
Figure
Timer/
57/170