Rainbow Electronics DS1957 - Manual (Page 22)

DS1957
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which is sufficient to operate the 1-Wire interface and to maintain the STOP mode of the microcomputer
and accelerator. Once the initial data is loaded through the 1-Wire interface, the bus master will send
either a Start Program or Continue Program command to the DS1957. Either of these commands will
turn on the internal P-Channel bypass to the diode in the parasitic power supply and enable the system
power controls to clear the STOP mode once the internal supply voltage rises above a certain trip point.
In addition to sending the Start Program or Continue Program command, the bus master also has to
activate the P-Channel transistor in its 1-Wire interface to bypass the 1-Wire pull-up resistor (see Data
Transfer and Control Function Flow Charts and command descriptions for details). Once the STOP mode
is cleared, the microcomputer and/or accelerator will begin to operate (period C). At a predetermined
time, the microcomputer and accelerator will both re-enter the STOP mode and wait for the bus master to
start communication.
During the time where power is supplied through the 1-Wire bus, it is impossible for the bus master and
the DS1957 to communicate. To inform each other about the progress of a computation, for example,
both the Master and the DS1957 have to agree on an accurate value of the time for computations. This
value is mutually agreed on during the initial data exchange and is based on the synchronization of the
True Time Clock in the DS1957 and the Real Time Clock in the bus master. By synchronizing to crystal
based clocks in the bus master and DS1957, it is possible to guarantee that the DS1957 will place the
microcomputer and accelerator into a STOP mode before the bus master begins the next data
communication.
POWER SITUATIONS ON THE 1-WIRE BUS Figure 9
NO COMMUNICATION,
NO POWER
A B C D
COMMUNICATION AND
PARASITIC POWER
FOR 1-WIRE INTERFACE
FULL POWER FOR
MICROCOMPUTER
AND ACCELERATOR
COMMUNICATION AND
PARASITIC POWER
FOR 1-WIRE INTERFACE
1-WIRE INTERFACE,
MICROCOMPUTER
AND ACCELERATOR
IN POWER DOWN
MODE
MICROCOMPUTER
AND ACCELERATOR
IN STOP MODE
NO 1-WIRE
COMMUNICATION
MICROCOMPUTER
AND ACCELERATOR
IN STOP MODE