Analog Devices ADuC812 - Manual (Page 32)

REV. B
ADuC812
–32–
Mode 2 (8-Bit Timer/Counter with Auto Reload)
Mode 2 configures the timer register as an 8-bit counter (TL0)
with automatic reload, as shown in Figure 28. Overflow from TL0
not only sets TF0, but also reloads TL0 with the contents of TH0,
which is preset by software. The reload leaves TH0 unchanged.
،12 CORE
CLK
TF0
CONTROL
P3.4/T0
TL0
(8 BITS)
INTERRUPT
C/T = 0
C/T = 1
RELOAD
TH0
(8 BITS)
GATE
P3.2/INT0
TR0
Figure 28. Timer/Counter 0, Mode 2
Mode 3 (Two 8-Bit Timer/Counters)
Mode 3 has different effects on timer 0 and timer 1. 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. This configuration is shown in Figure 29. TL0
uses the timer 0 control bits: C/T, Gate, TR0,
INT0, and TF0.
TH0 is locked into a timer function (counting machine cycles)
and takes over the use of TR1 and TF1 from timer 1. Thus, TH0
now controls the “Timer 1” interrupt. Mode 3 is provided for
applications requiring an extra 8-bit timer or counter.
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 interface as a Baud Rate Generator. In fact, it can be used,
in any application not requiring an interrupt from timer 1 itself.
،12 CORE
CLK
TL0
(8 BITS)
TF0
INTERRUPT
CONTROL
P3.4/T0
C/T = 0
C/T = 1
TH0
(8 BITS)
CORE
CLK/12
TR1
CORE
CLK/12
CONTROL
GATE
P3.2/INT0
TR0
TF1
INTERRUPT
Figure 29. Timer/Counter 0, Mode 3
TIMER/COUNTER 0 AND 1 OPERATING MODES
The following paragraphs describe the operating modes for timer/
counters 0 and 1. Unless otherwise noted, it should be assumed
that these modes of operation are the same for timer 0 as for timer 1.
Mode 0 (13-Bit Timer/Counter)
Mode 0 configures an 8-bit timer/counter with a divide-by-32
prescaler. Figure 26 shows mode 0 operation.
،12 CORE
CLK
P3.4/T0
GATE
P3.2/INT0
TR0
TF0
CONTROL
TL0
(5 BITS)
TH0
(8 BITS)
INTERRUPT
C/T = 0
C/T = 1
Figure 26. Timer/Counter 0, Mode 0
In this mode, the timer register is configured as a 13-bit register.
As the count rolls over from all 1s to all 0s, it sets the timer overflow
flag TF0. The overflow flag, TF0, can then be used to request an
interrupt. The counted input is enabled to the timer when TR0 = 1
and either Gate = 0 or
INT0 = 1. Setting Gate = 1 allows the timer
to be controlled by external input INT0, to facilitate pulsewidth
measurements. TR0 is a control bit in the special function regis-
ter TCON; Gate is in TMOD. The 13-bit register consists of all
eight bits of TH0 and the lower five bits of TL0. The upper three
bits of TL0 are indeterminate and should be ignored. Setting the
run flag (TR0) does not clear the registers.
Mode 1 (16-Bit Timer/Counter)
Mode 1 is the same as Mode 0, except that the timer register is
running with all 16 bits. Mode 1 is shown in Figure 27.
،12 CORE
CLK
TF0
CONTROL
P3.4/T0
TL0
(8 BITS)
TH0
(8 BITS)
INTERRUPT
C/T = 0
C/T = 1
GATE
P3.2/INT0
TR0
Figure 27. Timer/Counter 0, Mode 1