sh6622a SinoWealth Micro-Electronics Corp. Ltd, sh6622a Datasheet - Page 9

• Manufacturer Part Number: sh6622a
• Description: Mask 4-bit Microcontroller
• Manufacturer: SinoWealth Micro-Electronics Corp. Ltd

4.3. Timer0 mode register
The timer can be programmed in several different prescaler ratios by setting Timer Mode register (TM0). The 8-bit counter
counts prescaler overflow output pulses. The timer mode registers (TM0) are 3-bit registers used for timer control as shown in
table1. These mode registers select the input pulse sources into the timer.
Table 1. Timer 0 Mode Register ($02)
4.4. External Clock/Event T0 as Timer0 Source
When external clock/event input is used for TM0, it is synchronized with CPU system clock. Therefor the external source must
follow certain constrains. The output from T0M multiplex is T0C. It is sampled by system clock in instruction frame cycle.
Therefore it is necessary for T0C to be high at least 2 t
same as the system clock input. Therefore the requirements are as follows:
When other prescaler ratio is selected, the TM0 is scaled by the asynchronous ripple counter and so the prescaler output is
symmetrical.
Then:
The limitation is applied for T0 period time only. The pulse width is not limited by this equation. It is summarized as follows:
TM0.2
0
0
0
0
1
1
1
1
Where
The requirement is , therefore:
TM0.1
0
0
1
1
0
0
1
1
TM0.0
0
1
0
1
0
1
0
1
T0H = T0CH = T0 high time ≥ 2 t
T0L = T0CL = T0 low time ≥ 2 t
T0C high time = T0C low time =
T0 = Timer0 input period
N = prescaler value
T0 = Timer0 period ≥
N
*
2
T
0
≥ 2 t
Prescaler Divide Ratio
OSC
+ T
∆ , or T0 ≥
/2
/2
/2
/2
/2
/2
/2
/2
4
11
9
7
5
3
4
1
0
t *
OSC
OSC
N
and low at least 2 t
+
4
OSC
N
2
OSC
t *
∆
9
*
2
T
OSC
T0
+ T
+ T
N
∆
∆
+
2
Δ
T
2048 (initial)
OSC
Ratio N
512
128
32
. When prescaler ratio selects /20, T0C is the
8
4
2
1
SH6622A