11AAXXX/11LCXXX
If a command is terminated in any manner other than a
NoMAK/SAK combination, then the master must per-
form a standby pulse before beginning a new com-
mand, regardless of which device is to be selected.
3.0
3.1
BUS CHARACTERISTICS
Standby Pulse
When the master has control of SCIO, a standby pulse
can be generated by holding SCIO high for TSTBY. At
this time, the 11XX will reset and return to Standby
mode. Subsequently, a high-to-low transition on SCIO
(the first low pulse of the header) will return the device
to the active state.
Note: After a POR/BOR event occurs, a low-
to-high transition on SCIO must be gen-
erated before proceeding with communi-
cation, including a standby pulse.
An example of two consecutive commands is shown in
Figure 3-1. Note that the device address is the same
for both commands, indicating that the same device is
being selected both times.
Once a command is terminated satisfactorily (i.e., via
a NoMAK/SAK combination during the Acknowledge
sequence), performing a standby pulse is not required
to begin a new command as long as the device to be
selected is the same device selected during the previ-
ous command. However, a period of TSS must be
observed after the end of the command and before the
beginning of the start header. After TSS, the start
header (including THDR low pulse) can be transmitted
in order to begin the new command.
A standby pulse cannot be generated while the slave
has control of SCIO. In this situation, the master must
wait for the slave to finish transmitting and to release
SCIO before the pulse can be generated.
If, at any point during a command, an error is detected
by the master, a standby pulse should be generated
and the command should be performed again.
FIGURE 3-1:
CONSECUTIVE COMMANDS EXAMPLE
Standby Pulse(1)
Device Address
Start Header
SCIO
0 1 0 1 0 1 0 1
1 0 1 0 0 0 0 0
Device Address
Start Header
SCIO
0 1 0 1 0 1 0 1
1 0 1 0 0 0 0 0
Note 1: After a POR/BOR event, a low-to-high transition on SCIO is required to occur before the first
standby pulse.
When a standby pulse is not required (i.e., between
successive commands to the same device), a period of
3.2
Start Data Transfer
All operations must be preceded by a start header. The
start header consists of holding SCIO low for a period
of THDR, followed by transmitting an 8-bit ‘01010101’
code. This code is used to synchronize the slave’s
internal clock period with the master’s clock period, so
accurate timing is very important.
TSS must be observed after the end of the command
and before the beginning of the start header.
Figure 3-2 shows the waveform for the start header,
including the required Acknowledge sequence at the
end of the byte.
FIGURE 3-2:
START HEADER
SCIO
TSS
THDR Data ‘0’ Data ‘1’ Data ‘0’ Data ‘1’ Data ‘0’ Data ‘1’ Data ‘0’ Data ‘1’
MAK
NoSAK
2010 Microchip Technology Inc.
Preliminary
DS22067H-page 7
MICROCHIP [ MICROCHIP ]
