M48TMH1 Просмотр технического описания (PDF) - STMicroelectronics

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M48TMH1

5V PC REAL TIME CLOCK

STMicroelectronics 

M48T86

Table 2. Absolute Maximum Ratings (1)

Symbol

Parameter

Value

Unit

TA

Ambient Operating Temperature

0 to 70

°C

TSTG

Storage Temperature (VCC Off, Oscillator Off)

–40 to 85

°C

TSLD (2)

Lead Solder Temperature for 10 seconds

260

°C

VIO

Input or Output Voltages

–0.3 to 7.0

V

VCC

Supply Voltage

–0.3 to 7.0

V

PD

Power Dissipation

1

W

Note: 1. Stresses greater than those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress

rating only and functional operation of the device at these or any other conditions above those indicated in the operational section

of this specification is not implied. Exposure to the absolute maximum rating conditions for extended periods of time may affect

reliability.

2. Soldering temperature not to exceed 260°C for 10 seconds (total thermal budget not to exceed 150°C for longer than 30 seconds).

CAUTION: Negative undershoots below –0.3V are not allowed on any pin while in the Battery Back-up mode.

CAUTION: Do NOT wave solder SOIC to avoid damaging SNAPHAT sockets.

For the 28 lead SOIC, the battery/crystal package

part number is "M4T28-BR12SH1".

Automatic deselection of the device provides in-

surance that data integrity is not compromised

should VCC fall below specified Power-fail Dese-

lect Voltage (VPFD) levels. The automatic deselec-

tion of the device remains in effect upon power up

for a period of 200ms (max) after VCC rises above

VPFD, provided that the Real Time Clock is running

and the count down chain is not reset. This allows

sufficient time for VCC to stabilize and gives the

system clock a wake up period so that a valid sys-

tem reset can be established.

The block diagram in Figure 3 shows the pin con-

nections and the major internal functions of the

M48T86.

SIGNAL DESCRIPTION

VCC, VSS. DC power is provided to the device on

these pins.The M48T86 utilizes a 5V VCC.

SQW (Square Wave Output). During normal op-

eration (i.e. valid VCC), the SQW pin can output a

signal from one of 13 taps.The frequency of the

SQW pin can be changed by programming Regis-

ter A as shown in Table 10. The SQW signal can

be turned on and off using the SQWE bit (Register

B; bit 3). The SQW signal is not available when

VCC is less than VPFD.

AD0-AD7 (Multiplexed Bi-Directional Address/

Data Bus). 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, since the bus

change from address to data occurs during the in-

ternal RAM access time. Addresses must be valid

prior to the falling edge of AS, at which 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. 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.

AS (Address Strobe Input). 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.

MOT (Mode Select). The MOT pin offers the flex-

ibility to choose between two bus types. When

connected to VCC, Motorola bus timing is selected.

When connected to VSS or left disconnected, Intel

bus timing is selected. The pin has an internal pull-

down resistance of approximately 20K ohms.

3/23

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