Rainbow Electronics DS2741 - Manual (Page 7)

DS2741
Current Monitor and Accumulator with
Integrated Sense Resistor
_______________________________________________________________________________________ 7
Figure 4. I 2 C Timing Diagram
Registers
The DS2741 has 2-byte registers for current measure-
ment and accumulation. When the MSB of a 2-byte reg-
ister is read, both the MSB and LSB are latched and
held for the duration of the read data command to pre-
vent updates during the read and ensure synchroniza-
tion between the two register bytes. For consistent
results, always read the MSB and the LSB of a 2-byte
register during the same read data command sequence.
I 2 C Bus Interface
I 2 C Definitions
The following terminology is commonly used to
describe I
2 C data transfers.
Master Device: The master device controls the slave
devices on the bus. The master device generates
SCL clock pulses and START and STOP conditions.
Slave Devices: Slave devices send and receive
data at the master’s request.
Bus Idle or Not Busy: Time between STOP and
START conditions when both SDA and SCL are inac-
tive and in their logic-high states. When the bus is idle
it often initiates a low-power mode for slave devices.
START Condition: A START condition is generated
by the master to initiate a new data transfer with a
slave. Transitioning SDA from high to low, while SCL
remains high, generates a START condition. See
Figure 4 for applicable timing.
STOP Condition: A STOP condition is generated by
the master to end a data transfer with a slave.
Transitioning SDA from low to high, while SCL
remains high, generates a STOP condition. See
Figure 4 for applicable timing.
Repeated START Condition: The master can use a
repeated START condition at the end of one data
transfer to indicate that it will immediately initiate a
new data transfer following the current one.
Repeated STARTs are commonly used during read
operations to identify a specific memory address to
begin a data transfer. A repeated START condition
is issued identically to a normal START condition.
See Figure 4 for applicable timing.
Bit Write: Transitions of SDA must occur during the
low state of SCL. The data on SDA must remain
valid and unchanged during the entire high pulse of
SCL plus the setup and hold-time requirements (see
Figure 4). Data is shifted into the device during the
rising edge of the SCL.
Table 1. Register Map
ADDRESS
(HEX)
DESCRIPTION READ/WRITE
00h to 0Fh Reserved —
10h and 11h Current Accumulator Register R/ W
12h and 13h Reserved —
14h Temperature Register R
15h Reserved —
16h and 17h Current Register R
18h to FFh Reserved —
SCL
NOTE: TIMING IS REFERENCED TO V IL(MAX) AND V IH(MIN) .
SDA
STOP START REPEATED
START
t BUF
t HD:STA
t HD:DAT t SU:DAT
t SU:STO
t HD:STA
t SP
t SU:STA
t HIGH
t R
t F
t LOW