Rainbow Electronics DS28EA00 - Manual (Page 12)

DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
12 of 29
After the command code the master transmits a PIO Output Data byte that determines the new state of the PIO
output transistors. The first (least significant) bit is associated to PIOA; the next bit affects PIOB. The other 6 bits of
the new state byte do not have corresponding PIO pins. These bits should always be transmitted as "1"s. To switch
the output transistor on, the corresponding bit value is 0. To switch the output transistor off (non-conducting) the bit
must be 1. This way the bit transmitted as the new PIO output state arrives in its true form at the PIO pin.
To
protect the transmission against data errors, the master must repeat the PIO Output Data byte in its inverted form.
Only if the transmission was error-free will the PIO status change. The actual PIO transition to the new state occurs
with a delay of t
REH
+ x from the rising edge of the MS bit of the inverted PIO byte, as shown in Figure 8. The value
of "x" is approximately 0.2µs. To inform the master about the successful communication of the PIO byte, the
DS28EA00 transmits a confirmation byte with the data pattern AAh. While the MS bit of the confirmation byte is
transmitted, the DS28EA00 samples the state of the PIO pins, as shown in Figure 7, and sends it to the master.
The master can either continue writing more data to the PIO or issue a 1-Wire Reset to end the command.
Figure 8. PIO Access Write Timing Diagram
IO
PIO
MS 2 bits of inverted
PIO Output Data byte LS 2 bits of confir-
mation byte (AAh)
V
TH
t
REH
+x
CHAIN COMMAND [99h]
This command allows the master to put the DS28EA00 into one of the three Chain States, as shown in Figure 9.
The device powers up in the Chain OFF state. To transition a DS28EA00 from one state to another, the master
must send a suitable Chain Control byte after the Chain Command code. Only the codes 3Ch, 5Ah and 96h (true
form) are valid, assigned to OFF, ON, and DONE, in this sequence. This control byte is first transmitted in its true
form and then in its inverted form. If the Chain state change was successful, the master receives AAh confirmation
bytes. If the change was not successful (control byte transmission error, invalid control byte) the master will read
00h bytes instead.
Figure 9. Chain State Transition Diagram
Chain ON
Chain OFF
or POR
Chain DONE
These transitions are permissible, but
do not occur during normal operation.
OFF
Power-on
Reset (POR)
Chain DONE
Chain ON
ON DONE