Datasheet

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I
2
C High-Speed Mode (Hs Mode)
8-BitMasterCode00001xxx
S
IfPthen
FastorStandardMode
IfSr(dottedlines)
thenHigh-SpeedMode
1 6 7 8 92to5
2to51 6 7 8 9 1 6 7 8 9
2to5
SDA
SCL
SDA
SCL
Sr
=CurrentSourcePull-Up
=ResistorPull-Up
A=Acknowledge(SD LOWA )
N=NotAckno ledgew (SDAHIGH)
S START= Condition
P=STOP Con iiond t
Sr=RepeatedSTAR CondT iti no
N
t
H
t
H
High-SpeedMode
FastorStandardMode
t
FS
Sr P
7-BitSlaveAddress
R/W
A nx(8-BitDATA + A/N)
TSC2004
SBAS408E – JUNE 2007 – REVISED MARCH 2008
Serial data transfer format in High-Speed (Hs) mode meets the Fast or Standard (F/S) mode I
2
C bus
specification. Hs mode can only commence after the following conditions (all of which are in F/S mode) exist:
1. START condition (S)
2. 8-bit master code (00001xxx)
3. not-acknowledge bit (N)
Figure 33 shows this sequence in more detail. Hs-mode master codes are reserved 8-bit codes used only for
triggering Hs mode, and are not to be used for slave addressing or any other purpose. The master code
indicates to other devices that an Hs-mode transfer is about to begin and the connected devices must meet the
Hs mode specification. Because no device is allowed to acknowledge the master code, the master code is
followed by a not-acknowledge bit (N).
After the not-acknowledge bit (N) and SCL have been pulled up to a HIGH level, the master switches to Hs-mode
and enables (at time t
H
; shown in Figure 33 ) the current-source pull-up circuit for SCL. Because other devices
can delay the serial transfer before t
H
by stretching the LOW period of SCL, the master enables its
current-source pull-up circuit when all devices have released SCL, and SCL has reached a HIGH level, thus
speeding up the last part of the rise time of the SCL.
The master then sends a repeated START condition (Sr) followed by a 7-bit slave address with a R/ W bit
address, and receives an acknowledge bit (A) from the selected slave. After a repeated START (Sr) condition
and after each acknowledge bit (A) or not-acknowledge bit (N), the master disables its current-source pull-up
circuit. This disabling enables other devices to delay the serial transfer by stretching the LOW period of SCL. The
master re-enables its current-source pull-up circuit again when all devices have released, and SCL reaches a
HIGH level, which speeds up the last part of the SCL signal rise time.
Data transfer continues in Hs mode after the next repeated START (Sr), and only switches back to F/S mode
after a STOP condition (P). To reduce the overhead of the master code, it is possible that a master links a
number of Hs mode transfers, separated by repeated START conditions (Sr).
Figure 33. Complete High-Speed Mode Transfer
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