Z51F3220FNX Datasheet, PDF (111/312 Pages) Zilog, Inc. – Z8051 Series 8-Bit Microcontrollers

Z51F3220
Product Specification
11.4 Watch Timer
11.4.1 Overview
The watch timer has the function for RTC (Real Time Clock) operation. It is generally used for RTC design. The
internal structure of the watch timer consists of the clock source select circuit, timer counter circuit, output select
circuit, and watch timer control register. To operate the watch timer, determine the input clock source, output
interval, and set WTEN to ‘1’ in watch timer control register (WTCR). It is able to execute simultaneously or
individually. To stop or reset WT, clear the WTEN bit in WTCR register. Even if CPU is STOP mode, sub clock is
able to be so alive that WT can continue the operation. The watch timer counter circuits may be composed of 21-
bit counter which contains low 14-bit with binary counter and high 7-bit counter in order to raise resolution. In
WTDR, it can control WT clear and set interval value at write time, and it can read 7-bit WT counter value at read
time.
The watch timer supplies the clock frequency for the LCD driver (fLCD). Therefore, if the watch timer is disabled,
the LCD driver controller does not operate.
11.4.2 Block Diagram
fSUB
P
r
e
s
fx/64
M
U
fx
c _fx/128
X
a
l _fx/256
e
r
f WCK
14Bit
Binary Counter
fWCK /2¹⁴
WTCR WTEN
-
- WTIFR WTIN1 WTIN0 WTCK1 WTCK0
fLCD =1024 Hz
Timer counter
Clear
Match
WTCL
match
f WCK/(2¹⁴X (7 bit WTDR Value +1))
Comparator
fWCK /2¹⁴
fWCK /2¹³
fWCK /2 ⁷
MUX
WTIFR
Clear
2
INT_ACK
Reload
Match
WTCL
To interrupt
block
WTDR
Write case
WTCNT
Read case
WTCL WTDR6 WTDR5 WTDR4 WTDR3 WTDR2 WTDR1 WTDR0
- WTCNT6 WTCNT5 WTCNT4 WTCNT3 WTCNT2 WTCNT1 WTCNT0
Figure 11.5 Watch Timer Block Diagram
PS029902-0212
PRELIMINARY
108