Effect of MAN_SLAVE_ACK bit on EOM Handling
371
SNIU028A – February 2016 – Revised April 2016
Copyright © 2016, Texas Instruments Incorporated
PMBus Interface/I2C Interface
Table 10-2. Timing Parameters from Timing Diagrams
Parameter
Min
Max
Units
t
START
– Time from PMBUS_DATA low for Start signal to UNIT_BUSY bit
set
366
470
ns
t
SAR
– Time from PMBUS_CLK low on bit 8 to SLAVE_ADDR_READY bit
set
488
605
ns
t
DREQ1
– Time from PMBUS_CLK low on bit 8 of address byte to
DATA_REQUEST bit set
427
538
ns
t
ACKWRITE
– Time from write to ACK bit until UCD releases clock stretch
427
538
ns
t
DREQ2
– Time from write to ACK bit until DATA_REQUEST bit is set
ns
t
RPTSTRT
– Time from PMBUS_DATA low for Repeated Start to
RPT_START bit set
366
470
ns
t
DREQ3
– Time from PMBUS_CLK low on bit 8 of read byte to
DATA_REQUEST bit set
427
538
ns
t
TXBWRITE
– Time from PMBUS_CLK low on bit 8 to SLAVE_ADDR_READY
bit set
427
538
ns
t
DRDY
– Time from PMBUS_CLK low on bit 8 to DATA_RDY bit set
488
605
ns
t
EOM
– Time from PMBUS_CLK high for Stop signal to EOM and
DATA_RDY bits set, as well as PEC VALID and RD_BYTE_COUNT
loaded with correct value.
427
538
ns
Table 10-3.
PMBus/I2C edge which triggers change
Bit Field
Changed
Min(ns)
Max(ns)
SCL rise or fall
SCL_RAW set
or clear
244
336
SDA rise or fall
SDA_RAW set
or clear
244
336
CONTROL rise or fall
CONTROL_RA
W set or clear
244
336
ALERT rise or fall
ALERT_RAW
set or clear
244
336
CONTROL edge specified by CNTL_INT_EDGE
CONTROL_EDG
E
244
336
ALERT falling edge
ALERT_EDGE
244
336
SCL and SDA high for nominal 50 usec
BUS_FREE set
122
202
Table 10-4. Simple Timing Parameters (No Timing Diagram)
Interval
Min(ns)
Max(ns)
PMBST Bit Set to Interrupt Trigger
61
67
10.6 Effect of MAN_SLAVE_ACK bit on EOM Handling
Even though MAN_SLAVE_ACK primarily affects the handling of the beginning of the message, it also
changes how the end of the message is handled.
In both modes, the PMBus hardware is designed to stretch the clock until the firmware is done processing
the previous message.
When MAN_SLAVE_ACK is low, the firmware must ACK after the EOM. This tells the hardware that it is
OK to ack the next address automatically and put the new address value into the PMBHSA. The EOM
should not be ACKed until the firmware has read the PMBHSA for the message.
The next bit set in the status register will be either DATA_READY or DATA_REQUEST.