Specifications

52
3706C–MICRO–2/11
AT89LP3240/6440
11.1 Mode 0 – Variable Width Timer/Counter
Both Timers in Mode 0 are 8-bit Counters with a variable prescaler. The prescaler may vary from
1 to 8 bits depending on the PSC bits in TCONB, giving the timer a range of 9 to 16 bits.
By default the timer is configured as a 13-bit timer compatible to Mode 0 in the standard 8051.
Figure 11-1 shows the Mode 0 operation as it applies to Timer 1 in 13-bit mode. As the count
rolls
over from all “1”s to all “0”s, it sets the Timer interrupt flag TF1. The counter input is enabled
to the Timer when TR1 = 1 and either GATE1 = 0 or INT1
=1. Setting GATE1 = 1 allows the
Timer to be controlled by external input INT1
, to facilitate pulse width measurements. TR1 is a
control bit in the Special Function Register TCON. GATE1 is in TMOD. The 13-bit register con-
sists of all 8 bits of TH1 and the lower 5 bits of TL1. The upper 3 bits of TL1 are indeterminate
and should be ignored. Setting the run flag (TR1) does not clear the registers.
Note: RH1/RL1 are not required by Timer 1 during Mode 0 and may be used as temporary storage
registers.
Figure 11-1. Timer/Counter 1 Mode 0: Variable Width Counter
Mode 0 operation is the same for Timer 0 as for Timer 1, except that TR0, TF0, GATE0 and
INT0
replace the corresponding Timer 1 signals in Figure 11-1. There are two different C/T bits,
one for Timer 1 (TMOD.6) and one for Timer 0 (TMOD.2).
11.2 Mode 1 – 16-bit Auto-Reload Timer/Counter
In Mode 1 the Timers are configured for 16-bit auto-reload. The Timer register is run with all
16 bits. The 16-bit reload value is stored in the high and low reload registers (RH1/RL1). The
clock is applied to the combined high and low timer registers (TH1/TL1). As clock pulses are
received, the timer counts up: 0000H, 0001H, 0002H, etc. An overflow occurs on the FFFFH-to-
0000H transition, upon which the timer register is reloaded with the value from RH1/RL1 and the
overflow fla
g bit in TCON is set. See Figure 11-2. The reload registers default to 0000H, which
gives the full 16-bit timer period compatible with the standard 8051. Mode 1 operation is the
same for Timer/Counter 0.
Mode 0: Time-out Period
256 2
PSC0 1+
×
Oscillator Frequency
-------------------------------------------------------
TPS 1+()×=
OSC
T1 Pin
TR1
GATE1
INT1 Pin
TL1
(8 Bits)
Control
Interrupt
C/T = 0
C/T = 1
PSC1
TH1
(8 Bits)
TF1
÷TPS
Mode 1: Time-out Period
65536 RH0 RL0{,}–()
Oscillator Frequency
---------------------------------------------------------
TPS 1+()×=