Clock Timer; Configuration Of Clock Timer - Epson S1C63666 Technical Manual

4.9 Clock Timer

4.9.1 Configuration of clock timer

The S1C63666 has a built-in clock timer that uses OSC1 (crystal oscillator) as the source oscillator. The
clock timer is configured of an 8-bit binary counter that serves as the input clock, f
output from the prescaler. Timer data (128–16 Hz and 8–1 Hz) can be read out by the software.
Figure 4.9.1.1 is the block diagram for the clock timer.
OSC1
oscillation circuit
(f )
OSC1
Clock timer RUN/STOP signal
Ordinarily, this clock timer is used for all types of timing functions such as clocks.
4.9.2 Data reading and hold function
The 8 bits timer data are allocated to the address FF75H and FF76H.
<FF75H> D0: TM0 = 128 Hz
<FF76H> D0: TM4 = 8 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 S1C63666 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 read timing.)
Note: Since the low-order data is not held when the high-order data has previously been read, the low-
order data should be read first.
S1C63666 TECHNICAL MANUAL
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Clock Timer)
Data bus
256 Hz
Divider
Clock timer reset signal
Fig. 4.9.1.1 Block diagram for the clock timer
D1: TM1 = 64 Hz
D1: TM5 = 4 Hz
Clock timer
128 Hz–16 Hz
32 Hz, 8 Hz, 2 Hz, 1 Hz
Interrupt
control
D2: TM2 = 32 Hz
D2: TM6 = 2 Hz
EPSON
divided clock
OSC1
8 Hz–1 Hz
Interrupt
request
D3: TM3 = 16 Hz
D3: TM7 = 1 Hz
63