
S1C62740 TECHNICAL HARDWARE
EPSON
I-51
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Clock Timer)
Clock Timer
4.8
Configuration of
clock timer
The S1C62740 has a built-in clock timer as the source oscillator
for OSC1 (crystal oscillator). The clock timer is configured of a 8-bit
binary counter that serves as the input clock, a 256 Hz signal
output by the OSC1 oscillation circuit. Timer data (128–16 Hz and
8–1 Hz) can be read out by the software.
Figure 4.8.1 is the block diagram for the clock timer.
Ordinarily, this clock timer is used for all types of timing functions
such as clocks.
Data reading and
hold function
The 8 bits timer data are allocated to the address E3H and E4H.
E3H
D0: TM0 (128 Hz)
D1: TM1 (64 Hz)
D2: TM2 (32 Hz)
D3: TM3 (16 Hz)
E4H
D0: TM4 (8 Hz)
D1: TM5 (4 Hz)
D2: TM6 (2 Hz)
D3: TM7 (1 Hz)
Since the clock timer data has been allocated to two addresses, a
carry is generated from the low-order data within the count (TM0–
TM3: 128–16 Hz) to the high-order data (TM4–TM7: 8–1 Hz). When
this carry is generated between the reading of the low-order data
and the high-order data, a content combining the two does not
become the correct value (the low-order data is read as FFH and
the high-order data becomes the value that is counted up 1 from
that point).
The high-order data hold function in the S1C62740 is designed to
operate to avoid this. This function temporarily stops the counting
up of the high-order data (by carry from the low-order data) at the
point where the low-order data has been read and consequently the
time during which the high-order data is held is the shorter of the
two indicated here following.
1. Period until it reads the high-order data.
2. 0.48–1.5 msec (varies due to the timing of the reading)
When the high-order data has previously been read, since the low-order
data is not held, you should be sure to first read from the low-order data.
Fig. 4.8.1
Block diagram for the clock timer
128–16 Hz
Data bus
32 Hz, 8 Hz, 2 Hz, 1 Hz
256 Hz
Clock timer reset signal
OSC1
oscillation
circuit
Interrupt request
Interrupt
control
8–1 Hz
1/2–1/4 Hz
Clock timer
Watchdog
timer
Initial
reset
Watchdog timer
reset signal
Note: