Rainbow Electronics DS2890 - Manual (Page 17)

DS2890
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RESUME COMMAND [A5H]
In a typical application the DS2890 may be accessed several times to complete a control adjustment. In a
multi-drop environment this means that the 64-bit ROM sequence of a Match ROM command has to be
repeated for every access. To maximize the data throughput in a multi-drop environment the Resume
Command function was implemented. As shown in Figure 24, this function checks the status of the RC
flag and, if it is set, directly transfers control to the potentiometer functions, similar to a Skip ROM
command. The only way to set the RC flag is through successfully executing the Match ROM, Search
ROM, Conditional Search ROM, or Overdrive Match ROM command. Once the RC flag is set, the
device can repeatedly be accessed through the Resume Command function. Accessing another device on
the bus will clear the RC flag, preventing two or more devices from simultaneously responding to the
Resume Command function.
POTENTIOMETER FUNCTION EXAMPLE
At regular speed with an auxiliary supply (V
DD
within range): turn on the charge pump, set the wiper
position to mid-point, increment the wiper twice, and decrement the wiper once.
MASTER MODE DATA (LSB FIRST) COMMENTS
TX Reset Reset Pulse (480 - 960 ms)
RX Presence Presence Pulse
TX CCh Issue Skip ROM Command
TX 55h Issue Write Control Register Command
TX 4Ch Issue Control Register value for WN=0, CPC=1
RX Read back Control Register value (4Ch) and verify
TX 96h Issue Release Code to update Control Register
RX
If 0’s are read, update was successful; if 1’s are read,
the update failed
TX Reset Reset Pulse (480 - 960 ms)
RX Presence Presence Pulse
TX CCh Issue Skip ROM Command
TX 0Fh Issue Write Position Command
TX 7Fh Write Wiper Position value
RX Read back Wiper Position byte and verify
TX 96h Issue Release Code to update Wiper Position
RX
If 0’s are read, update was successful; if 1’s are read,
the update failed
TX Reset Reset Pulse
RX Presence Presence Pulse
TX CCh Issue Skip ROM Command