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PDF VT82887 Data sheet ( Hoja de datos )
| Número de pieza | VT82887 | |
| Descripción | Real Time Clock | |
| Fabricantes | VIA | |
| Logotipo |  |
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VIA Technologies, Inc.
VT82887
Real Time Clock
FEATURES
• Drop-in replacement for IBM AT computer
clock/calendar.
• Pin configuration closely matches the
DS12887
• Totally nonvolatile with over 10 years of
operation in the absence of power
· Self-contained subsystem includes lithium,
quartz and support circuitry
• Counts seconds, minutes, hours, days, day
of the week, date, month and year with leap
year compensation
• Binary or BCD representation of time,
calendar and alarm
• 12- or 24-hour clock with AM and PM in 12-
hour mode
• Daylight Savings Time option
• Intel bus timing
• Multiplex bus for pin efficiency
• Interfaced with software as 128 RAM
locations
- 14 bytes of clock and control registers
- 114 bytes of general purpose RAM
• Programmable square wave output signal
• Bus-compatible interrupt signals (IRQ#)
• Three interrupts are separately software-
maskable and testable
- Times-of-day alarm once/second to
once/day
- Periodic rates from 122 µs to 500 ms
- End of clock update cycle
DESCRIPTION
The VT82887 Real Time Clock is designed to
be a direct replacement for the DS12887. The
VT82887 is identical in form, fit and function
to the DS12887. It has 114 bytes of general
purpose RAM. Access to this RAM space is
OPERATION
determined by the logic level presented on
AD6 during the address portion of an access
cycle. An external crystal and battery are the
only components required to maintain time-of-
day and memory status in the absence of
power. A complete description of operating
conditions, electrical characteristics, bus
timing and pin descriptions follows.
PIN ASSIGNMENT
VT82887 24 PIN DIP
GND
NC
NC
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
GND
1
2
3
4
5
6
7
8
9
10
11
12
24 VCC
23 SQW
22 NC
21 RCLR#
20 NC
19 IRQ#
18 RESET#
17 RD#
16 NC
15 WR#
14 AS
13 CS#
PIN DESCRIPTION
AD0-AD7
NC
CS#
AS
WR#
RD#
RESET#
IRQ#
SQW
VCC
GND
RCLR#
- Multiplexed Address/Data Bus
- No Connection
- Chip Select
- Address Strobe
- Write Strobe
- Read Strobe
- Reset Input
- Interrupt Request Output
- Square Wave Output
- +5 Volt Supply
- Ground
- RAM Clear
1
1 page  
VIA Technologies, Inc.
VT82887
Real Time Clock
contain the RTC time, calendar and alarm
data, and four bytes which are used for
control and status. All 128 bytes can be
directly written or read except for the
following:
1. Registers C and D are read-only.
FIGURE 2: ADDRESS MAP VT82887
TIME, CALENDAR AND ALARM
LOCATIONS
The time and calendar information is obtained
by reading the appropriate memory bytes.
The time, calendar and alarm are set
or initialized by writing the appropriate RAM
bytes. The contents of the ten time, calendar
and alarm bytes can be either Binary or
Binary-Coded Decimal (BCD) format. Before
0 00
14 Bytes
Clock and Control
Status Registers
13 OD
14 0E
114 Bytes
Storage
Registers
127 7F
writing the internal time, calendar and alarm
registers, the SET bit in Register B should be
written to a logic one to prevent updates from
occurring while access is being attempted. In
addition to writing the ten time, calendar and
alarm registers in a selected format (binary or
2. Bit 7 of Register A is read-only.
3. The high order bit of the seconds byte is
read-only.
The contents of four registers (A, B, C and D)
are described in the “Register” section.
BCD), the data mode bit (DM) of Register B
must be set to the appropriate logic level. All
ten time, calendar and alarm bytes must use
the same data mode. The SET bit in Register
B should be cleared after time, calendar or
alarm have been written to allow the real time
clock to update the time and calendar bytes.
Once initialized, the real time clock makes all
updates in the selected mode. The data mode
cannot be changed without reinitializing the
Binary or BCD Input
0 SECONDS 00
1 SECONDS ALARM 01
2 MINUTES 02
3 MINUTES ALARM 03
4 HOURS 04
5 HOURS ALARM 05
6 DAY OF THE WEEK 06
7 DAY OF THE MONTH 07
8 MONTH 08
9 YEAR 09
10 REGISTER A 0A
11 REGISTER B 0B
12 REGISTER C 0C
13 REGISTER D 0D
ten data bytes. Table 2 shows the binary and
BCD formats of the ten time, calendar and
alarm locations. The 24-12 bit cannot be
changed without reinitializing the hour
locations. When the 12-hour format is
selected, the high order bit of the hours byte
5
5 Page 
VIA Technologies, Inc.
VT82887
Real Time Clock
VOLTAGE ON ANY PIN RELATIVE TO GROUND -0.3V TO +7.0V
OPERATING TEMPERATURE
0°C TO 70°C
STORAGE TEMPERATURE
-40°C TO +70°C
SOLDERING TEMPERATURE
260°C FOR 10 SECONDS
*This is a stress rating only and functional operation of the device at these or any other conditions
above those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS (0°C TO 70°C)
PARAMETER
SYMBOL MIN TYP MAX
Power Supply Voltage
Input Logic 1
Input Logic 0
VCC 4.5
VIH 2.2
VIL -0.3
5.0 5.5
VCC+0.3
+0.8
UNITS
V
V
V
NOTES
1
1
1
DC ELECTRICAL CHARACTERISTICS (0°C TO 70°C, VCC = 4.5 TO 5.5V)
PARAMETER
SYMBOL MIN TYP MAX UNITS
Power Supply Current
Input Leakage
ICC1
5 10 mA
IIL -1.0
+1.0 µA
I/O Leakage
Input Current
Output @ 2.4V
Output @ 0.4V
Write Protect Voltage
ILO -1.0
+1.0 µA
IMOT
-1.0
+500
µA
IOH -1.0
mA
IOL 4.0 mA
VTP 4.0 4.25 4.5
V
NOTES
2
3
4
3
1,5
1
CAPACITANCE (tA = 25°C)
PARAMETER
SYMBOL
Input Capacitance
Output Capacitance
CIN
COUT
MIN
TYP
MAX
5
7
UNITS
pF
pF
NOTES
AC ELECTRICAL CHARACTERISTICS (0°C TO 70°C, VCC = 4.5V TO 5.5V)
PARAMETER
SYMBOL MIN TYP MAX UNITS
Cycle Time
Pulse Width, DS/E Low or
RD/WR# High
tCYC
PWEL
385
150
DC ns
ns
Pulse Width, DS/E High or PWEH
RD/WR# Low
125
ns
Input Rise and Fall Time
tR, tF
30 ns
NOTES
11
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| PDF Descargar | [ Datasheet VT82887.PDF ] | |
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