M48T201Y-85MH1(2004) Просмотр технического описания (PDF) - STMicroelectronics
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M48T201Y-85MH1 Datasheet PDF : 33 Pages
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M48T201Y, M48T201V
OPERATION
Automatic backup and write protection for an ex-
ternal SRAM is provided through VOUT, ECON, and
GCON pins. (Users are urged to insure that voltage
specifications, for both the SUPERVISOR chip
and external SRAM chosen, are similar.) The
SNAPHAT® containing the lithium energy source
is used to retain the RTC and RAM data in the ab-
sence of VCC power through the VOUT pin. The
chip enable output to RAM (ECON) and the output
enable output to RAM (GCON) are controlled dur-
ing power transients to prevent data corruption.
The date is automatically adjusted for months with
less than 31 days and corrects for leap years (valid
until 2100). The internal watchdog timer provides
programmable alarm windows.
The nine clock bytes (7FFFFh-7FFF9h and
7FFF1h) are not the actual clock counters, they
are memory locations consisting of BiPORT™
READ/WRITE memory cells within the static RAM
array. Clock circuitry updates the clock bytes with
current information once per second. The informa-
tion can be accessed by the user in the same man-
ner as any other location in the static memory
array. Byte 7FFF8h is the clock control register.
This byte controls user access to the clock infor-
mation and also stores the clock calibration set-
ting.
Byte 7FFF7h contains the watchdog timer setting.
The watchdog timer can generate either a reset or
an interrupt, depending on the state of the Watch-
dog Steering Bit (WDS). Bytes 7FFF6h-7FFF2h
include bits that, when programmed, provide for
clock alarm functionality. Alarms are activated
when the register content matches the month,
date, hours, minutes, and seconds of the clock
registers. Byte 7FFF1h contains century informa-
tion. Byte 7FFF0h contains additional flag informa-
tion pertaining to the watchdog timer, the alarm
condition, the battery status and square wave out-
put operation. 4 bits are included within this regis-
ter (RS0-RS3) that are used to program the
Square Wave Output Frequency (see Table
7., page 18). The M48T201Y/V also has its own
Power-Fail Detect circuit. This control circuitry
constantly monitors the supply voltage for an out
of tolerance condition. When
ance, the circuit write protects
tVhCeCTIisMEouKtEoEfPtoElRer®-
register data and external SRAM, providing data
security in the midst of unpredictable system oper-
ation. As VCC falls below the Battery Back-up
Switchover Voltage (VSO), the control circuitry au-
tomatically switches to the battery, maintaining
data and clock operation until valid power is re-
stored.
Address Decoding
The M48T201Y/V accommodates 19 address
lines (A0-A18) which allow direct connection of up
to 512K bytes of static RAM. Regardless of SRAM
density used, timekeeping, watchdog, alarm, cen-
tury, flag, and control registers are located in the
upper RAM locations. All TIMEKEEPER registers
reside in the upper RAM locations without conflict
by inhibiting the GCON (output enable RAM) signal
during clock access. The RAM's physical locations
are transparent to the user and the memory map
looks continuous from the first clock address to the
upper most attached RAM addresses.
Table 2. Operating Modes
Mode
VCC
E
G
Deselect
VIH
X
WRITE
READ
4.5V to 5.5V
or
3.0V to 3.6V
VIL
X
VIL
VIL
READ
VIL
VIH
Deselect
VSO to VPFD (min)(1)
X
X
Deselect
≤ VSO(1)
X
X
Note: X = VIH or VIL; VSO = Battery Back-up Switchover Voltage
1. See Table 14., page 27 for details.
W
DQ7-DQ0
Power
X
High-Z
Standby
VIL
DIN
VIH
DOUT
Active
Active
VIH
High-Z
Active
X
High-Z
CMOS Standby
X
High-Z
Battery Back-Up
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