Epson S1C63558 4.8 Clock Timer, 4.8.1 Configuration of clock timer, 4.8.2 Data reading and hold function, OSC1, Divider, control, request, Data bus, Interrupt, Interrupt

CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Clock Timer)

4.8 Clock Timer

4.8.1 Configuration of clock timer

The S1C63558 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, fOSC1 divided clock output from the prescaler. Timer data (128–16 Hz and 8–1 Hz) can be read out by the software.

Figure 4.8.1.1 is the block diagram for the clock timer.

Data bus

OSC1				Clock timer
		256 Hz
oscillation circuit	Divider		128 Hz–16 Hz		8 Hz–1 Hz
(fOSC1)

32 Hz, 8 Hz, 2 Hz, 1 Hz

Clock timer reset signal	Interrupt	Interrupt
Clock timer RUN/STOP signal	control	request
Fig. 4.8.1.1 Block diagram for the clock timer

Ordinarily, this clock timer is used for all types of timing functions such as clocks.

4.8.2 Data reading and hold function

The 8 bits timer data are allocated to the address FF79H and FF7AH.

<FF79H>	D0: TM0	= 128 Hz	D1: TM1	= 64 Hz	D2: TM2	= 32 Hz	D3: TM3	= 16 Hz
<FF7AH>	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 S1C63558 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.

S1C63558 TECHNICAL MANUAL EPSON 57