sh66p31b SinoWealth Micro-Electronics Corp. Ltd, sh66p31b Datasheet - Page 13

• Manufacturer Part Number: sh66p31b
• Description: Otp 1k 4-bit Micro-controller
• Manufacturer: SinoWealth Micro-Electronics Corp. Ltd

7.3. External Clock/Event T0 as Timer0 Source
When external clock/event T0 input as Timer0 source, it is synchronized with the CPU system clock. The external source must
follow certain constraints. The system clock samples it in instruction frame cycle. Therefore it is necessary to be high (at least 2
t
The requirement is as follows
When another prescaler ratio is selected, the TM0 is scaled by the asynchronous ripple counter, so that the prescaler output is
symmetrical. Then:
Where:
The requirement is:
So, the limitation is applied for the T0 period time only. The pulse width is not limited by this equation. It is summarized as follows:
Systems Register $1C:
T0E: T0 signal edge
0: Increment on low-to-high transition T0 pin (Power on initial)
1: Increment on high-to-low transition T0 pin
T0S: T0 signal source
0: System clock (Power on initial)
1: Transition on T0 pin
OSC
Address
$1C
) and low (at least 2 t
Bit 3
-
-
-
-
-
T0 = Timer0 input period
T0H (T0 high time) ≥ 2 * t
T0L (T0 low time) ≥ 2 * t
N = prescaler value
T0
T0
N
*
2
high
T0
=
Timer0
≥
OSC
Bit 2
time
2
-
-
-
-
-
t *
). When the prescaler ratio selects/2
OSC
period
=
T0
+
∆
low
Bit 1
T0S
T
≥
X
X
0
1
time
4
t *
OSC
OSC
OSC
=
or
+ ∆ T;
N
N
+ ∆ T
+
Bit 0
T0E
*
2
2
0
X
X
1
T0
*
∆
T
T0
≥
R/W
W
W
W
W
W
4
13
t *
∆ T = 20ns
OSC
Bit0: T0 signal edge
Bit1: T0 signal source
Increment on low-to-high transition T0 pin (Power-on initial)
Increment on high-to-low transition T0 pin
System clock (Power-on initial)
Transition on T0 pin
0
, it is the same as the system clock input.
N
+
2
*
∆
T
Remarks
SH66P31B