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PDF VT82885 Data sheet ( Hoja de datos )
| Número de pieza | VT82885 | |
| Descripción | Real Time Clock | |
| Fabricantes | ETC | |
| Logotipo |  |
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VIA Technologies, Inc.
VT82885
Real Time Clock
FEATURES
• Drop-in replacement for IBM AT computer
clock/calendar.
• Pin configuration closely matches the
DS12887, DS12885and DS12885Q
• 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 interrpts 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
• Optional 28-pin PLCC surface mount
package
DESCRIPTION
The VT82885 Real Time Clock is designed
to be a direct replacement for the DS12885.
The VT82885 is identical in form, fit and
function to the DS12885. It has 114 bytes of
general purpose RAM. Access to this RAM
space is 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
GND
X1
X2
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 VBAT
19 IRQ#
18 RESET#
17 RD#
16 NC
15 WR#
14 AS
13 CS#
VT82885 24 PIN DIP
GS
4 X X N N V Q N 26
5 2 1 D C CC W C 25
AD0
AD1
3 2 1 28 27
6 24
RCLR#
VBAT
AD2 7
23 IRQ#
AD3 8
22 RESET#
AD4 9
21 RD#
AD5 10
20 GND
NC
13 14 15 16 17
WR#
11
ANAGCAN
DCDNS S C
19
18
6 7 D#
VT82885 28-PIN PLCC
PIN DESCRIPTION
AD0-AD7
NC
CS#
AS
- Multiplexed Address/Data Bus
- No Connection
- Chip Select
- Address Strobe
1
1 page  
VIA Technologies, Inc.
VT82885
Real Time Clock
E. Periodic Interrupt Flag (PF) bit is cleared
to zero.
F. The device is not accessible until
RESET# is returned high.
G. Alarm Interrupt Flag (AF) bit is cleared to
zero.
H. IRQ# pin is in the high impedence state.
I. Square Wave Output Enable (SQWE)
bit is cleared to zero.
J. Update Ended Interrupt Enable (UIE) is
cleared to zero.
In a typical application RESET# can be
connected to VCC. This connection will allow
the VT82885 to go in and out of power fail
without affecting any of the control registers.
ADDRESS MAP
The address map of the VT82885 is shown
in Figure 2. The address map consists of
114 bytes of user RAM, 10 bytes of RAM
that 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 the following:
1. Registers C and D are read-only.
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.
FIGURE 2: ADDRESS MAP VT82885
0 00
14 Bytes
Clock and Control
Status Registers
13 OD
14 0E
114 Bytes
Storage
Registers
127 7F
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
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, calen-
dar and alarm bytes can be either Binary or
Binary-Coded Decimal (BCD) format. Be-
fore writing the internal time, calendar and
alarm registers, the SET bit in Register B
5
5 Page 
VIA Technologies, Inc.
VT82885
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
ILO -1.0
+1.0 µA
Input Current
IMOT
-1.0
+500
µA
Output @ 2.4V
Output @ 0.4V
Write Protect Voltage
IOH -1.0
IOL 4.0
VTP 4.0 4.25 4.5
mA
mA
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
NOTES
11
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| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet VT82885.PDF ] | |
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