DS1347 Maxim, DS1347 Datasheet - Page 13

• Manufacturer Part Number: DS1347
• Description: The DS1347 SPI-compatible real-time clock (RTC) contains a real-time clock/calendar and 31 x 8 bits of static random-access memory (SRAM)
• Manufacturer: Maxim

microcontroller, is active only during address and data
transfer to any device on the SPI bus. The inactive clock
polarity is usually programmable on the microcontroller
side of the SPI interface. In the device, input data is
latched on the positive edge, and output data is shifted
out on the negative edge. There is one clock cycle for
each bit transferred. Address and data bits are trans-
ferred in groups of eight.
The SPI protocol allows for one of four combinations of
serial clock phase and polarity from the microcontroller,
through a 2-bit selection in its SPI Control register. The
clock polarity is specified by the CPOL Control bit,
which selects active-high or active-low clock, and has
no significant effect on the transfer format. The clock
phase control bit, CPHA, selects one of two different
transfer formats. The clock phase and polarity must be
identical for the master and the slave. For the device,
set the control bits to CPHA = 1 and CPOL = 1. This
configures the system for data out to be launched on
Figure 1a. Single Write
Figure 2b. Burst Write
CS
SCLK
DIN
DOUT
*ONLY ONE ADDRESS/COMMAND BYTE IS REQUIRED PER BURST TRANSACTION.
Low-Current, SPI-Compatible Real-Time Clock
R/W
A6
CS
SCLK
DIN
DOUT
1
ADDRESS/COMMAND BYTE*
______________________________________________________________________________________
R/W
1
1
A6
HIGH IMPEDANCE; NO ACTIVITY ON DOUT LINE DURING WRITES.
ADDRESS/COMMAND BYTE
1
A5
1
A4
1
A3
HIGH IMPEDANCE; NO ACTIVITY ON DOUT LINE DURING WRITES.
D7
A2
D6
A1
D5
1
DATA BYTE 1
D4
D3
D7
the negative edge of SCLK and data in to be sampled
on the positive edge. With CPHA equal to 1, CS can
remain low between successive data byte transfers,
allowing burst-mode data transfers to occur.
Address and data bytes are shifted MSB first into DIN
of the device, and out of DOUT. Data is shifted out at
the negative edge of SCLK, and shifted in or sampled
at the positive edge of SCLK. Any transfer requires an
address/command byte followed by one or more
bytes of data. Data is transferred out of DOUT for a
read operation, and into DIN for a write operation.
DOUT transmits data only after an address/command
byte specifies a read operation; otherwise, it is high
impedance.
Data transfer write timing is shown in Figure 1. Data
transfer read timing is shown in Figure 2. Detailed read
and write timing is shown in Figure 3.
D2
D6
D1
D5
D0
DATA BYTE
D4
D3
D7
D2
D6
D5
D1
DATA BYTE N
D4
D0
D3
D2
D1
D0
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