EZ80F91MCU Datasheet, PDF (187/396 Pages) Zilog, Inc. – eZ80Acclaim-TM Flash Microcontrollers

eZ80F91 MCU
Product Specification
168
• Write values to the RTC alarm registers to set the appropriate alarm condi-
tions
• Write to RTC_CTRL to clear RTC_UNLOCK; clearing the RTC_UNLOCK bit
resets and enables the clock divider
Real-Time Clock Registers
The Real-Time Clock registers are accessed via the address and data buses
using I/O instructions. The RTC_UNLOCK control bit controls access to the RTC
count registers. When unlocked (RTC_UNLOCK = 1), the RTC count is disabled
and the count registers are Read/Write. When locked (RTC_UNLOCK = 0), the
RTC count is enabled and the count registers are Read Only. The default, at
RESET, is for the RTC to be locked.
Real-Time Clock Seconds Register
This register contains the current seconds count. The value in the RTC_SEC reg-
ister is unchanged by a RESET. The current setting of BCD_EN determines
whether the values in this register are binary (BCD_EN = 0) or binary-coded deci-
mal (BCD_EN = 1). Access to this register is Read Only if the RTC is locked and
Read/Write if the RTC is unlocked. See Table 80.
Table 80. Real-Time Clock Seconds Register
(RTC_SEC = 00E0h)
Bit
7
6
5
4
3
2
1
0
Reset
X
X
X
X
X
X
X
X
CPU Access
R/W* R/W* R/W* R/W* R/W* R/W* R/W* R/W*
Note: X = Unchanged by RESET; R/W* = Read Only if RTC locked, Read/Write if RTC unlocked.
Binary-Coded-Decimal Operation (BCD_EN = 1)
Bit
Position
[7:4]
TEN_SEC
[3:0]
SEC
Value Description
0–5 The tens digit of the current seconds count.
0–9 The ones digit of the current seconds count.
Binary Operation (BCD_EN = 0)
Bit
Position
[7:0]
SEC
Value Description
00h– The current seconds count.
3Bh
PS019209-0504
PRELIMINARY
Real-Time Clock