EVAL-ADUC834QS Analog Devices Inc, EVAL-ADUC834QS Datasheet - Page 59

• Manufacturer Part Number: EVAL-ADUC834QS
• Manufacturer: Analog Devices Inc

Specifications of EVAL-ADUC834QS

• Lead Free Status / RoHS Status: Not Compliant

BAUD RATE GENERATION USING TIMER 1 AND TIMER 2
Timer 1 Generated 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:
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 three running modes. In the most
typical application, it is configured for timer operation, in the
Autoreload Mode (high nibble of TMOD = 0100 binary). In
that case, the baud rate is given by the formula:
A very low baud rate can also be achieved with Timer 1 by
leaving the Timer 1 interrupt enabled, configuring the timer to
run as a 16-bit timer (high nibble of TMOD = 0100 binary), and
using the Timer 1 interrupt to do a 16-bit software reload.
Table XXXI shows some commonly-used baud rates and how
they might be calculated from a core clock frequency of 1.5728
MHz and 12.58 MHz using Timer 1. Generally speaking, a 5%
error is tolerable using asynchronous (start/stop) communications.
Ideal
Baud
9600
1600
1200
1200
REV. A
Modes 1
Mode 1
Table XXXI. Commonly Used Baud Rates, Timer 1
and
Core
CLK
12.58
12.58
12.58
1.57
and Mode Baud Rate
3
Baud Rate
OSC. FREQ. IS DIVIDED BY 2, NOT 12.
NOTE AVAILABILITY OF ADDITIONAL
EXTERNAL INTERRUPT
*THE CORE CLOCK IS THE OUTPUT OF THE PLL (SEE "ON-CHIP PLL")
TRANSITION
SMOD
Value
1
1
1
1
T2EX
DETECTOR
PIN
PIN
CORE
CLK*
T2
3
=
(
2
TH1-Reload
Value
–7 (F9H)
–27 (E5H)
–55 (C9H)
–7 (F9H)
SMOD
2
⁄
32
=
C/ T2 = 0
C/ T2 = 1
)
32 12 256
×
(
EXEN2
2
Timer Overflow Rate
×
SMOD
CONTROL
CONTROL
Figure 56. Timer 2, UART Baud Rates
Actual
9362
1627
1192
1170
(
Baud
1
TR2
×
f
CORE
−
EXF 2
TH
1
%
Error
2.5
1.1
0.7
2.5
)
RCAP2L
(8 BITS)
TL2
)
TIMER 2
INTERRUPT
–59–
RCAP2H
(8 BITS)
Timer 2 Generated Baud Rates
Baud rates can also be generated using Timer 2. Using Timer 2
is similar to using Timer 1 in that the timer must overflow 16
times before a bit is transmitted/received. Because Timer 2 has
a 16-bit Autoreload Mode, a wider range of baud rates is pos-
sible using Timer 2.
Therefore when Timer 2 is used to generate baud rates, the
timer increments every two clock cycles and not every core
machine cycle as before. Thus, it increments six times faster
than Timer 1, and therefore baud rates six times faster are pos-
sible. Because Timer 2 has a 16-bit autoreload capability, very
low baud rates are still possible.
Timer 2 is selected as the baud rate generator by setting the
TCLK and/or RCLK in T2CON. The baud rates for transmit
and receive can be simultaneously different. Setting RCLK and/or
TCLK puts Timer 2 into its baud rate generator mode as shown
in Figure 56. In this case, the baud rate is given by the formula:
Table XXXII shows some commonly used baud rates and
how they might be calculated from a core clock frequency of
1.5728 MHz and 12.5829 MHz using Timer 2.
Ideal
Baud
19200
9600
1600
1200
9600
1600
1200
Mode 1 and Mode
Mode 1
TH2
Table XXXII. Commonly Used Baud Rates, Timer 2
RELOAD
OVERFLOW
and Mode Baud Rate
TIMER 2
Core
CLK
12.58
12.58
12.58
12.58
1.57
1.57
1.57
3
3
RCAP2H
Value
–1 (FFH)
–1 (FFH)
–1 (FFH)
–2 (FEH)
–1 (FFH)
–1 (FFH)
–1 (FFH)
Baud Rate
1
1
OVERFLOW
2
TIMER 1
0
0
0
1
=
RCLK
RCAP2L
Value
–20 (ECH)
–41 (D7H)
–164 (5CH) 2398
–72 (B8H)
–5 (FBH)
–20 (ECH)
–41 (D7H)
TCLK
(
=
1 16
16
16
32
SMOD
)
×
×
(
(
RX
CLOCK
TX
CLOCK
65536
Timer Overflow Rate
ADuC834
Actual
Baud
19661
9591
1199
9830
1658
1199
f
CORE
2
−
RCAP H L
2
%
Error
2.4
0.1
0.1
0.1
2.4
2.4
0.1
)
)