11AAXXX/11LCXXX
3.0
3.1
BUS CHARACTERISTICS
Standby Pulse
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.
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
for both commands, indicating that the same device is
being selected both times.
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.
When the master has control of SCIO, a standby pulse
can be generated by holding SCIO high for T
STBY
. 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.
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 T
SS
must be
observed after the end of the command and before the
beginning of the start header. After T
SS
, the start
header (including T
HDR
low pulse) can be transmitted
in order to begin the new command.
FIGURE 3-1:
CONSECUTIVE COMMANDS EXAMPLE
MAK
NoSAK
Standby Pulse
(1)
Start Header
Device Address
MAK
SAK
MAK
NoSAK
DS22067E-page 7
SCIO
0 1 0 1 0 1 0 1
NoMAK
SAK
T
SS
MAK
NoSAK
1 0 1 0 0 0 0 0
MAK
SAK
Data ‘1’
Start Header
Device Address
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.
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 T
HDR
, 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.
When a standby pulse is not required (i.e., between
successive commands to the same device), a period of
T
SS
must be observed after the end of the command
and before the beginning of the start header.
including the required Acknowledge sequence at the
end of the byte.
FIGURE 3-2:
SCIO
T
SS
START HEADER
T
HDR
Data ‘0’
Data ‘1’
Data ‘0’
Data ‘1’
Data ‘0’
Data ‘1’
Data ‘0’
©
2008 Microchip Technology Inc.
Preliminary
MICROCHIP [ MICROCHIP TECHNOLOGY ]
