m48t86 STMicroelectronics, m48t86 Datasheet - Page 9

• Manufacturer Part Number: m48t86
• Description: 5v Pc Real Time Clock
• Manufacturer: STMicroelectronics

Operation
Signal description
V
SQW (square wave output)
AD0-AD7 (multiplexed bi-directional address/data bus)
AS (address strobe input)
CC
, V
SS
The M48T86 clock is driven by a quartz-controlled oscillator with a nominal frequency of
32,768 Hz. The devices are tested not to exceed 23 ppm (parts per million) oscillator
frequency error at 25°C, which equates to approximately ±1 minute per month. Automatic
deselection of the device ensures the data integrity is not compromised should V
below specified Power-fail Deselect Voltage (V
automatic deselection of the device remains in effect upon power up for a period of 200ms
(max) after V
count-down chain is not reset. This allows sufficient time for V
system clock a wake-up period so that a valid system reset can be established.
The block diagram in
functions of the M48T86.
DC power is provided to the device on these pins.The M48T86 uses a 5V V
During normal operation (e.g., valid V
taps. The frequency of the SQW pin can be changed by programming Register A as shown
in
(Register B; Bit 3). The SQW signal is not available when V
The M48T86 provides a multiplexed bus in which address and data information share the
same signal path. The bus cycle consists of two stages; first the address is latched, followed
by the data. Address/Data multiplexing does not slow the access time of the M48T86,
because the bus change from address to data occurs during the internal RAM access time.
Addresses must be valid prior to the falling edge of AS (see
time the M48T86 latches the address present on AD0-AD7. Valid WRITE data must be
present and held stable during the latter portion of the R/W pulse (see
In a READ cycle, the M48T86 outputs 8 bits of data during the latter portion of the DS pulse.
The READ cycle is terminated and the bus returns to a high impedance state upon a high
transition on R/W.
A positive going pulse on the Address Strobe (AS) input serves to demultiplex the bus. The
falling edge of AS causes the address present on AD0-AD7 to be latched within the
M48T86.
Table 4 on page
CC
rises above V
18. The SQW signal can be turned on and off using the SQWE Bit
Figure 4 on page 8
PFD
, provided that the Real Time Clock is running and the
CC
), the SQW pin can output a signal from one of 13
shows the pin connections and the major internal
PFD
) levels (see
CC
Figure 5 on page
CC
is less than V
Figure 14 on page
to stabilize and gives the
Figure 6 on page
CC
PFD
.
11), at which
.
CC
27). The
fall
11).
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