Rainbow Electronics DS28EA00 - Manual (Page 11)

DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
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RECALL EEPROM [B8h]
This command recalls the TH and TL alarm trigger values and configuration data from backup EEPROM into their
respective locations in the scratchpad. After having transmitted the command code, the master may issue read
time slots to monitor the completion of the recall process. Recall is completed when the master reads 1-bits instead
of 0-bits. The recall occurs automatically at power-up, not requiring any activity by the master.
PIO ACCESS READ [F5h]
This command reads the PIO logical status and reports it together with the state of the PIO Output Latch in an
endless loop. A PIO Access Read can be terminated at any time with a 1-Wire Reset. PIO Access Read can be
executed in the Chain ON and Chain DONE state. While the device is in Chain ON or Chain DONE state, the PIO
output latch states will always read out as 1s; the PIO pin state may not be reported correctly.
PIO Status Bit Assignment
b7 b6 b5 b4 b3 b2 b1 b0
Complement of b3 to b0
PIOB Output
Latch State
PIOB Pin
State
PIOA Output
Latch State
PIOA Pin
State
The state of both PIO channels is sampled at the same time. The first sampling occurs during the last (most
significant) bit of the command code F5h. The PIO status is then reported to the bus master. While the master
receives the last (most significant) bit of the PIO status byte, the next sampling occurs and so on until the master
generates a 1-Wire Reset. The sampling occurs with a delay of t
REH
+x from the rising edge of the MS bit of the
previous byte, as shown in Figure 7. The value of "x" is approximately 0.2µs.
Figure 7. PIO Access Read Timing Diagram
IO
MS 2 bits of
previous byte LS 2 bits of PIO
Status byte
V
TH
Sampling Point
t
REH
+x
Notes:
1
The "previous byte" could be the command code or the data byte resulting from the previous PIO sample.
2 The sample point timing also applies to the PIO Access Write command, with the "previous byte" being the
write confirmation byte (AAh).
PIO ACCESS WRITE [A5h]
The PIO Access Write command writes to the PIO output latches, which control the pulldown transistors of the PIO
channels. In an endless loop this command first writes new data to the PIO and then reads back the PIO status.
This implicit read-after-write can be used by the master for status verification. A PIO Access Write can be termi-
nated at any time with a 1-Wire Reset. The PIO Access Write command is ignored by the device while in Chain ON
or Chain DONE state.
PIO Output Data Bit Assignment
b7 b6 b5 b4 b3 b2 b1 b0
X X X X X X PIOB PIOA