DS1646 查看數據表（PDF） - Dallas Semiconductor -> Maxim Integrated

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DS1646

Nonvolatile Timekeeping RAM

Dallas Semiconductor -> Maxim Integrated 

DS1646/DS1646P

DESCRIPTION

The DS1646 is a 128K x 8 nonvolatile static RAM with a

full function Real Time Clock (RTC) which are both ac-

cessible in a Byte–wide format. The nonvolatile time-

keeping RAM is function equivalent to any JEDEC stan-

dard 128K x 8 SRAM. The device can also be easily

substituted in ROM, EPROM and EEPROM sockets

providing read/write nonvolatility and the addition of the

real time clock function. The real time clock information

resides in the eight uppermost RAM locations. The RTC

registers contain year, month, date, day, hours, min-

utes, and seconds data in 24–hour BCD format. Correc-

tions for the day of the month and leap year are made

automatically. The RTC clock registers are double buff-

ered to avoid access of incorrect data that can occur

during clock update cycles. The double buffered sys-

tem also prevents time loss as the timekeeping count-

down continues unabated by access to time register

data. The DS1646 also contains its own power–fail cir-

cuitry which deselects the device when the VCC supply

is in an out of tolerance condition. This feature prevents

loss of data from unpredictable system operation

brought on by low VCC as errant access and update

cycles are avoided.

PACKAGES

The DS1646 is available in two packages (32–pin DIP

module and 34–pin PowerCap module). The 32–pin

Dip style module integrated the crystal, lithium energy

source, and silicon all in one package. The 34–pin Pow-

erCap Module Board is designed with contacts for con-

BLOCK DIAGRAM DS1646 Figure 1

nection to a separate PowerCap (DS9034PCX) that

contains the crystal and battery. This desgin allows the

PowerCap to be mounted on top of the DS1646P after

the completion of the surface mount process. Mounting

the PowerCap after the surface mount process pre-

vents damage to the crystal and battery due to high tem-

peratures required for solder reflow. The PowerCap is

keyed to prevent reverse insertion. The PowerCap

Module Board and PowerCap are ordered separately

and shipped in seperate containers. The part number

for the PowerCap is DS9034PCX.

CLOCK OPERATIONS–READING THE

CLOCK

While the double buffered register structure reduces the

chance of reading incorrect data, internal updates to the

DS1646 clock registers should be halted before clock

data is read to prevent reading of data in transition.

However, halting the internal clock register updating

process does not affect clock accuracy. Updating is

halted when a one is written into the read bit, the seventh

most significant bit in the control register. As long as a

one remains in that position, updating is halted. After a

halt is issued, the registers reflect the count, that is day,

date, and time that was current at the moment the halt

command was issued. However, the internal clock reg-

isters of the double buffered system continue to update

so that the clock accuracy is not affected by the access

of data. All of the DS1646 registers are updated simul-

taneously after the clock status is reset. Updating is

within a second after the read bit is written to zero.

32.768 KHz

OSCILLATOR AND

CLOCK COUNTDOWN

CHAIN

CLOCK

REGISTERS

PFO

VCC

+

VBAT

POWER MONITOR,

SWITCHING, AND

WRITE PROTECTION

POWER GOOD

128K x 8 NVSRAM

CE

WE

OE

A0–A16

DQ0–DQ7

031698 2/12

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