P89C738ABB View Datasheet(PDF) - Philips Electronics
Part Name
Description
MFG CO.
'P89C738ABB' PDF : 64 Pages View PDF
Philips Semiconductors
8-bit Flash microcontrollers
Product specification
P89C738; P89C739
10.2.2 CAPTURE MODE
In the capture mode (see Fig.11) there are two options
which are selected by bit EXEN2 in T2CON. If EXEN2 = 0,
then Timer 2 is a 16-bit timer/counter which on overflow
sets bit TF2 (Timer 2 overflow bit). TF2 can be used to
generate an interrupt. If EXEN2 = 1, Timer 2 operates as
above, with the added feature that a HIGH-to-LOW
transition at the external input T2EX causes the current
value in Timer 2 registers (TL2 and TH2) to be captured
into registers RCAP2L and RCAP2H, respectively. The
HIGH-to-LOW transition of T2EX also causes bit EXF2 in
T2CON to be set. EXF2 can be used to generate an
interrupt.
10.2.3 AUTOMATIC RELOAD MODE
In the automatic reload mode (see Fig.12) there are two
options which are selected by bit EXEN2 in SFR T2CON.
If EXEN2 = 0, then a Timer 2 overflow sets TF2 and
causes the Timer 2 registers to be reloaded with the 16-bit
value in registers RCAP2L and RCAP2H, which are preset
by software.
If EXEN2 = 1, Timer 2 operates as above, with the added
feature that a HIGH-to-LOW transition at the external input
T2EX triggers the 16-bit reload and sets EXF2.
The baud rate generation by Timer 1 and/or Timer 2 is
used for the Serial Port in Mode 1 and Mode 3. The baud
rate generation mode is similar to the automatic reload
mode, in that a roll-over in TH2 causes the Timer 2
registers to be reloaded with the 16-bit value in registers
RCAP2L and RCAP2H, which are preset by software.
The baud rates for the Serial Port in Modes 1 and 3 are
determined by Timer 2 overflow rate as follows:
Baud rate = T----i--m-----e---r----2-----o--1-v---6e---r--f--l-o----w------r--a---t--e-
Timer 2 can be configured for either ‘timer’ or ‘counter’
operation. Normally, as a timer it would increment every
machine cycle (thus at 1⁄12fclk). As a baud rate generator,
however it increments every state time (thus at 1⁄2fclk).
The baud rate is given by the formula:
Baud rate = 3----2-----×------[--6---5----5---3---6-----–------(--R----f-C-c--l-Ak----P----2----H----,---R-----C----A----P----2---L----)---]--
In this mode an overflow of Timer 2 does not set TF2.
If EXEN2 = 1, a HIGH-to-LOW transition at pin T2EX sets
EXF2 and can be used to generate an interrupt.
10.2.4 BAUD RATE GENERATOR MODE
The baud rate generator mode (see Fig.13) is selected by
RCLK = 1 and/or TCLK = 1 in SFR T2CON. Overflows of
either Timer 2 or Timer 1 can be used independently for
generating baud rates for transmit and receive.
handbook, full pagewidth
OSC
12
C/T2 = 0
T2 PIN
C/T2 = 1
transition
detector
T2EX PIN
control
TR2
capture
TL2
(8 BITS)
TH2
(8 BITS)
RCAP2L RCAP2H
control
EXEN2
TF2
Timer 2
interrupt
EXF2
MLA608
Fig.11 Timer 2 in capture mode.
1998 Apr 07
22
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