DS2790 Maxim Integrated Products, DS2790 Datasheet - Page 28

• Manufacturer Part Number: DS2790
• Description: Programmable 1-Cell Li-Ion Fuel Gauge and Protector
• Manufacturer: Maxim Integrated Products

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Both the TXD and RXD FIFOs are flushed when a new command byte is accepted (command handshaking is
enabled and the TWSCMD register is not busy, or when command handshaking is disabled). In the TWS FIFO
register (TWSFIF), LRX[3:0] reports the number of received bytes waiting in the RXD FIFO and LTX[3:0] reports
the number of bytes in the TXD FIFO to be transmitted.
Timeouts and Clock Extending
Clock extending during a DS2790 receive event (master write), is applied to delay the rising edge of SCL just
before the ACK symbols after the command byte is sent, and to any ACK symbols thereafter. If the RXD FIFO is
full, the clock low time just prior to the ACK symbol will be extended until a timeout occurs or the RXD FIFO has
been read and is no longer full.
Clock extending during a DS2790 transmit event (master read), is applied to delay the rising edge of SCL just after
the ACK symbol following the address, and to any ACK symbols thereafter. If the TXD FIFO is empty, the clock low
time just after the ACK symbol will be extended until a timeout occurs of the TXD FIFO has been written and is no
longer empty.
The T
its internal state machine. These timers allow the bus to remain available even after bus fault conditions such as
device hot swapping. Without the timers, such scenarios could result in a bus lock-up preventing all further
communication. The T
clock. If the timer ever reaches the T
data line is also released. The T
note that the timer is not reset during a REPEATED START condition. The timer counts while the TWS is holding
the clock low. The timer does not count when a master or other slave device is holding the clock low. The timer is
stopped on a STOP condition. If the timer times out (nominal 15ms), the clock line is released, followed by the data
line.
The T
using the TLS_DIS bit. The TOUT_LONG bit in the TWSCFG register allows the nominal value of the timeout
conditions to be increased by a factor of four.
Command Codes
The DS2790 has two reserved command codes: a software power on reset (POR) of the IC, and an instruction to
begin program loading over the 2-wire interface. Each command code is first enabled by transmitting the
Command Enable (FEh) followed directly by the command instruction. There are no associated data bytes with
either command. Any 2-wire communication between the two instructions negates the operation. See the MAXQ
Family User's Guide: DS2790 Supplement for the 2-wire programming procedure. These command codes are fixed
inside the DS2970 and cannot be altered. System firmware should avoid using FEh as a command code during
during device operation.
Table 11. 2-Wire Interface Command Codes
Command Enable
4
Programming
COMMAND
Soft POR
available
TIMEOUT
Request
TIMEOUT
timer can be disabled using the TTO_DIS bit in the TWSCFG register, while T
and T
LOW:SEXT
TIMEOUT
Repeated FEh
00h-FCh, FFh
HEX CODE
timers analyze the 2-Wire bus for timeout conditions, and can cause the TWS to reset
FEh
FDh
timer begins counting on the falling edge of clock, and is reset on the rising edge of
LOW:SEXT
TIMEOUT
timer is reset whenever a START condition occurs on the bus. Specifically
Enable soft POR or program command.
Causes a reset of the part.
Initiates programming over 2-wire interface.
Defined by application firmware.
value (nominal 30ms), the clock line is released, after a short delay the
DS2790 Programmable 1-Cell Li-Ion Fuel Gauge and Protector
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PURPOSE
LOW:SEXT
can be disabled