Clock Source - Epson S1C88655 Technical Manual

11.4 Clock Source

There are four clock sources and selection is made
by setting the two bits of the clock source selection
register SCSx0 and SCSx1 as shown in table below.
Table 11.4.1 Clock source
SCSx1 SCSx0
1 1
1 0
0 1
0 0
This register setting is invalid in clock synchronous
slave mode and the external clock input from the
___________
SCLKx terminal is used.
When the "programmable timer " is selected, the
underflow signal of the programmable timer 1 for
Ch. 0 or timer 7 for Ch. 1 is divided by 2 and the
divided signal is used as the clock source.
With respect to the transfer rate setting, see Chapter
13, "Programmable Timer".
At initial reset, the synchronous clock is set to
"f /16".
OSC3
Programmable timer underflow signal
(Ch. 0: timer 1, Ch. 1: timer 7)
S1C88655 TECHNICAL MANUAL
Clock source
Programmable timer 1 (Ch. 0)
Programmable timer 7 (Ch. 1)
f / 4
OSC3
f / 8
OSC3
f / 16
OSC3
OSC3
f
OSC3
oscillation Divider
circuit
1/2
(Clock synchronous slave mode)
SCLKx
Fig. 11.4.1 Division of the synchronous clock
Whichever clock is selected, the signal is further
divided by 16 and then used as the synchronous
clock.
Furthermore, external clock input is used as is for
___________
SCLKx in clock synchronous slave mode.
When the divided signal of the OSC3 oscillation
circuit is made the clock source, it is necessary to
turn the OSC3 oscillation ON, prior to using the
serial interface.
A time interval of several msec to several 10 msec,
from the turning ON of the OSC3 oscillation circuit
to until the oscillation stabilizes, is necessary, due to
the oscillation element that is used. Consequently,
you should allow an adequate waiting time after
turning ON of the OSC3 oscillation, before starting
transmitting/receiving of serial interface. (The
oscillation start time will vary somewhat depending
on the oscillator and on the externally attached parts.
Refer to the oscillation start time example indicated
in Chapter 19, "Electrical Characteristics".)
At initial reset, the OSC3 oscillation circuit is set to
ON status.
1/4
1/8
1/16
Selector
1/16
EPSON
11 SERIAL INTERFACE
Synchro-
Selector
nous clock
75