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INTERNAL SPECIFICATIONS
93
EXF2 : Timer/counter 2 external flag bit which is set when the T2EX pin level (bit 1 of
port 1) is changed from “1” to “0” at EXEN2=1. This flag serves as the timer
interrupt 2 request signal. When an interrupt is generated, this flag must be reset
to “0” by software.
TF2 : Timer/counter 2 internal flag bit which is set when a carry signal is generated by
timer/counter 2 in 16-bit auto reload mode or capture mode. This flag serves as
the timer interrupt 2 request signal. When an interrupt is generated, this flag
must be reset to “0” by software.
4.5.3.3 Timer/counter 2 operation modes
Timer/counter 2 operation modes are set by combinations of the CP/RL2, TCLK, and RCLK
bits in timer 2 control register (T2CON 0C8H) shown in Table 4-13. The timer modes are listed
in Table 4-14.
Table 4-13 Timer 2 control register (T2CON 0C8H)
Bit
Flag
Set
76543210
TF2 EXF2 RCLK TCLK EXEN2 TR2 C/T2 CP/RL2
•• •
Table 4-14 Timer/counter 2 modes
RCLK TCLK CP/ RL2 TR2
0001
0011
RCLK + TCLK = 1 × 1
×××0
Mode
16-bit auto reload
16-bit capture
Baud rate generator
All operations stopped
4.5.3.3.1 16-bit auto reload mode
16-bit auto reload mode is set by making the circuit connection shown in Figure 4-20 by setting
RCLK=0, TCLK=0, and CP/RL2=0 as the bit conditions in timer 2 control register (T2CON).
Timer/counter 2 operates in the following way when 16-bit auto reload mode is set. When a
timer/counter 2 carry signal is generated, or when the signal applied to the T2EX pin (bit 1
of port 1) is changed from level “1” to “0”, the reload data in the RCAP2L and RCAP2H
registers is preset in L2 and TH2 of timer/counter 2. The timer/counter thus starts counting
from this preset value.
The timer/counter 2 carry signal is set in internal timer flag 2 (TF2), and the T2EX change is
set in external timer flag 2 (EXF2). The TF2 and EXF2 serve as the timer interrupt 2 request
signals with an interrupt call being made to address 43 (2BH) if the timer interrupt 2 has been
enabled. If an interrupt routine is commenced, the TF2 and EXF2 flags must be reset to “0”
by software.