UPSD3254 STMICROELECTRONICS [STMicroelectronics], UPSD3254 Datasheet - Page 57

• Manufacturer Part Number: UPSD3254
• Description: Flash Programmable System Devices with 8032 Microcontroller Core
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Figure 24. Timer/Counter Mode 3: Two 8-bit Counters
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.
Mode 3. Timer 1 in Mode 3 simply holds its count.
The effect is the same as setting TR1 = 0.
Timer 0 in Mode 3 establishes TL0 and TH0 as two
separate counters. The logic for Mode 3 on Timer
0 is shown in Figure 24. TL0 uses the Timer 0 con-
trol Bits: C/T, GATE, TR0, INT0, and TF0. TH0 is
locked into a timer function (counting machine cy-
cles) and takes over the use of TR1 and TF1 from
Timer 1. Thus, TH0 now controls the “Timer 1“ In-
terrupt.
Mode 3 is provided for applications requiring an
extra 8-bit timer on the counter. With Timer 0 in
Mode 3, an uPSD325X devices can look like it has
three Timer/Counters. When Timer 0 is in Mode 3,
Timer 1 can be turned on and off by switching it out
of and into its own Mode 3, or can still be used by
the serial port as a baud rate generator, or in fact,
in any application not requiring an interrupt.
Timer 2
Like Timers 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. It has three operating modes: capture,
INT0 pin
Gate
T0 pin
f
f
OSC
OSC
TR0
÷ 12
÷ 12
C/T = 0
C/T = 1
TR1
UPSD3254A, UPSD3254BV, UPSD3253B, UPSD3253BV
Control
Control
autoload, and baud rate generator, which are se-
lected by bits in the T2CON as shown in Table 41.
In the Capture Mode there are two options 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 Over-
flow Bit, which can be used to generate an inter-
rupt. 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 causes the cur-
rent 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 25.
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 26. The Baud Rate Generation
Mode is selected by (RCLK, RCLK1)=1 and/or
(TCLK, TCLK1)=1. It will be described in conjunc-
tion with the serial port.
(8 bits)
(8 bits)
TH1
TL0
TF0
TF1
Interrupt
Interrupt
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