Handshake Solutions
HT80C51 User Manual
Peripheral Modules – Timers 0 and 1
Page 26 of 132
© Philips Electronics N.V. 2005
5.2.
Timers 0 and 1
This module comprises two 16bit timers/counters: timer0 and timer1. Both can be configured to oper-
ate either as timers or event counters.
In the “Timer” function, the register is incremented every timer clock cycle (clock input t01_clk_i).
Thus, if the operation of the CPU is synchronized to the same clock, one can think of it as counting
machine cycles of the CPU.
In the “Counter” function, the register is incremented in response to a 1-to-0 transition at its corre-
sponding external input pin, t0_count_i or t1_count_i. By design there are no restrictions on the
duty cycle or the frequency of the external input signals. However, depending on the standard cell
library, that is used, and the actual layout some maximum limits will apply.
5.2.1.
Options
This module can be enabled (ordered) by using option HT80C51_T01 .
5.2.2.
Special function registers (TMOD TCON TL0 TL1 TH0 TH1)
TMOD
Timer/Counter Mode Control
addr = 89H
reset value = 00H
bits
7
6
5
4
3
2
1
0
GATE1
C/T1
T1M1
T1M0
GATE0
C/T0
T0M1
T0M0
bit
symbol
Function
TMOD.7
GATE1
1:
0:
Timer 1 gating control
Timer/Counter 1 is enabled only while input pin t01_int1_n_i is high
and TR1 (TCON) is 1.
Timer/Counter 1 is enabled if TR1 is set.
TMOD.6
C/T1
1:
0:
Timer 1 operation selection
counter operation (clock source is input pin t1_count_i)
timer operation (clock source is the clock input t01_clk_i)
TMOD.5
TMOD.4
T1M1
T1M0
00:
01:
10:
11:
Timer 1 mode selection
8048 timer mode, TL1 serves as a 5bit prescaler
16bit timer/counter: TH1 and TL1 are cascaded; no prescaler
8bit auto-reload timer/counter: TH1 holds the value which is loaded into
TL1 each time it overflows
stopped
TMOD.3
GATE0
1:
0:
Timer 0 gating control
Timer/Counter 0 is enabled only while input pin t01_int0_n_i is high
and TR0 (TCON) is 1.
Timer/Counter 1 is enabled if TR0 is set.
TMOD.2
C/T0
1:
0:
Timer 0 operation selection
counter operation (clock source is input pin t0_count_i)
timer operation (clock source is the clock input t01_clk_i)
TMOD.1
TMOD.0
T0M1
T0M0
00:
01:
10:
11:
Timer 0 mode selection
8048 timer mode, TL0 serves as a 5bit prescaler
16bit timer/counter: TH0 and TL0 are cascaded; no prescaler
8bit auto-reload timer/counter: TH0 holds the value which is loaded into
TL0 each time it overflows
TL0 is an 8bit timer/counter controlled by standard timer 0 control bits.
TH0 is a further 8bit timer controlled by timer 1 control bits.
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