sh66k31c SinoWealth Micro-Electronics Corp. Ltd, sh66k31c Datasheet - Page 13

• Manufacturer Part Number: sh66k31c
• Description: Mask 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 a certain constraint. 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 asynchronous ripple counter scales the TM0, 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
T0S: T0 signal source
Address
OSC
$1C
) and low (at least 2 t
0: Increment on low-to-high transition T0 pin (Power on initial)
1: Increment on high-to-low transition T0 pin
0: System clock (Power on initial)
1: Transition on T0 pin
Bit 3
-
-
-
-
-
T0H (T0 high time) ≥ 2 * t
T0L (T0 low time) ≥ 2 * t
N = prescaler value
T0
T0
N
*
2
high
T0
=
Timer0
≥
Bit 2
time
2
OSC
-
-
-
-
-
t *
OSC
). When the prescaler ratio selects /2
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
1
X
X
0
T0
*
∆
T
T0
≥
R/W
4
W
W
W
W
W
13
t *
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
N
+
0
, it is the same as the system clock input.
2
*
∆
; ∆T = 20ns
T
T0 = Timer0 input period
Remarks
SH66K31C