DS1251 Maxim, DS1251 Datasheet - Page 5

• Manufacturer Part Number: DS1251
• Description: The DS1251 4096K NV SRAM with Phantom Clock is a fully static nonvolatile RAM (organized as 512K words by 8 bits) with a built-in real-time clock
• Manufacturer: Maxim

from the timekeeping registers can proceed. The next 64 cycles will cause the phantom clock to either
receive or transmit data on DQ0, depending on the level of the
locations outside the memory block can be interleaved with
recognition sequence or data transfer sequence to the phantom clock.
PHANTOM CLOCK REGISTER INFORMATION
The phantom clock information is contained in eight registers of 8 bits, each of which is sequentially
accessed 1 bit at a time after the 64-bit pattern recognition sequence has been completed. When updating
the phantom clock registers, each register must be handled in groups of 8 bits. Writing and reading
individual bits within a register could produce erroneous results. These read/write registers are defined in
Figure 2.
Data contained in the phantom clock register is in binary-coded decimal format (BCD). Reading and
writing the registers is always accomplished by stepping through all eight registers, starting with bit 0 of
register 0 and ending with bit 7 of register 7.
PHANTOM CLOCK REGISTER DEFINITION Figure 1
NOTE: THE PATTERN RECOGNITION IN HEX IS C5, 3A, A3, 5C, C5, 3A, A3, 5C. THE ODDS OF THIS PATTERN BEING ACCIDENTALLY
DUPLICATED AND CAUSING INADVERTENT ENTRY TO THE PHANTOM CLOCK IS LESS THAN 1 IN 10
THE PHANTOM CLOCK LSB TO MSB.
5 of 20
CE
OE
cycles without interrupting the pattern
pin or the
19
. THIS PATTERN IS SENT TO
WE
pin. Cycles to other