UPSD3212C, UPSD3212CV
Mode 2. Mode 2 configures the Timer register as
an 8-bit Counter (TL1) with automatic reload, as
shown in Figure 23. Overflow from TL1 not only
sets TF1, but also reloads TL1 with the contents of
TH1, which is preset by software. The reload
leaves TH1 unchanged. Mode 2 operation is the
same for Timer/Counter 0.
1-to-0 transition at external input T2EX causes the
current value in the Timer 2 registers, TL2 and
TH2, to be captured into registers RCAP2L and
RCAP2H, respectively. In addition, the transition
at T2EX causes Bit EXF2 in T2CON to be set, and
EXF2 like TF2 can generate an interrupt. The Cap-
ture Mode is illustrated in Figure 24, page 56.
Timer 2
In the Auto-reload Mode, there are again two op-
tions, which are selected by bit EXEN2 in T2CON.
If EXEN2 = 0, then when Timer 2 rolls over it not
only sets TF2 but also causes the Timer 2 regis-
ters to be reloaded with the 16-bit value in regis-
ters RCAP2L and RCAP2H, which are preset by
software. If EXEN2 = 1, then Timer 2 still does the
above, but with the added feature that a 1-to-0
transition at external input T2EX will also trigger
the 16-bit reload and set EXF2. The Auto-reload
Mode is illustrated in Standard Serial Interface
(UART) Figure 25, page 56. The Baud Rate Gen-
eration Mode is selected by (RCLK, RCLK1) = 1
and/or (TCLK, TCLK1) = 1. It will be described in
conjunction with the serial port.
Like Timer 0 and 1, Timer 2 can operate as either
an event timer or as an event counter. This is se-
lected by Bit C/T2 in the special function register
T2CON (see Table 40). It has three operating
modes: Capture, Auto-reload, and Baud Rate
Generator (see Table 41, page 55), which are se-
lected by bits in the T2CON as shown in Table 42,
page 55. In the Capture Mode there are two op-
tions which are selected by Bit EXEN2 in T2CON.
if EXEN2 = 0, then Timer 2 is a 16-bit timer or
counter which upon overflowing sets Bit TF2, the
Timer 2 overflow bit, which can be used to gener-
ate an interrupt. If EXEN2 = 1, then Timer 2 still
does the above, but with the added feature that a
Figure 23. Timer/Counter Mode 2: 8-bit Auto-reload
f
÷ 12
OSC
C/T = 0
C/T = 1
TL1
(8 bits)
TF1
Interrupt
T1 pin
Control
TR1
Gate
INT1 pin
TH1
(8 bits)
AI06623
Table 40. Timer/Counter 2 Control Register (T2CON)
7
6
5
4
3
2
1
0
TF2
EXF2
RCLK
TCLK
EXEN2
TR2
C/T2
CP/RL2
54/152
STMICROELECTRONICS [ ST ]
