pc87591l National Semiconductor Corporation, pc87591l Datasheet - Page 371

• Manufacturer Part Number: pc87591l
• Description: Lpc Mobile Embedded Controllers
• Manufacturer: National Semiconductor Corporation

Revision 1.07
Host-Controlled Modules and Host Interface
Century Register (CEN)
Location: Programmable Index
Type: R/W
6.2.16 BCD and Binary Formats
6.2.17 Usage Hints
1. Read bit 7 of CRD register at each system power-up to validate the contents of the RTC registers and the CMOS RAM.
2. Change the backup battery while normal operating power is present, and not in backup mode, to maintain valid time and
3. A rechargeable NiCd battery may be used instead of a non-rechargeable Lithium battery. This is the preferred solution
4. A supercap capacitor may be used instead of the normal Lithium battery. In a portable system, typically, the V
6.2.18 RTC General-Purpose RAM Map
Bit
Name
Reset
Seconds
Minutes
Hours
Day
Date
Month
Year
Century
7-0
Bit
When this bit is 0, the contents of these registers and the CMOS RAM are questionable. This bit is reset when the backup
battery voltage is too low. The voltage level at which this bit is reset is below the minimum recommended battery voltage,
2.4V. Although the RTC oscillator may function properly and the register contents may be correct at lower than 2.4V, this
bit is reset since correct functionality cannot be guaranteed. System BIOS may use a checksum method to revalidate
the contents of the CMOS-RAM. The checksum byte should be stored in the same CMOS RAM.
register information. If a low leakage capacitor is connected to V
for portable systems, where small components are essential.
is always present because the power management stops the system before its voltage falls to low. A supercap capacitor
in the range of 0.047F-0.47F should be able to supply the power during a battery replacement.
Parameter
Century Data. Values may be 00 to 99 in BCD format or 00 to 63 in binary format.
0E
00
7
0
1. Battery-backed 111-byte RAM (114 3 overlaid registers).
16
16
Index
Index
- 7F
- 7F
00 to 59
00 to 59
12-hour mode:01 to 12 (a.m.); 81 to 92 (p.m.)
24-hour mode:00 to 23
01 to 07 (Sunday = 01)
01 to 31
01 to 12 (January = 01)
00 to 99
00 to 99
16
16
1
6
0
Battery-backed general-purpose 111-byte RAM.
Battery-backed general-purpose 128-byte RAM.
BCD Format
Table 69. Extended RAM Map
Table 68. Standard RAM Map
5
0
Description
371
4
0
Century Data
Description
Description
(Continued)
BAT
, the battery may be changed in backup mode.
00 to 3B
00 to 3B
12-hour mode:01 to 0C (a.m.); 81 to 8C (p.m.)
24-hour mode:00 to 17
01 to 07
01 to 1F
01 to 0C
00 to 63
00 to 63
3
0
2
0
Binary Format
1
0
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SB
voltage
0
0