S
Address Rd
A
1
7
1
1
DATA_REQUEST
Write to TXBUF
EOM
Write to ACK
Byte
8
A
1
Byte
8
A
1
Byte
8
Byte
8
A
1
A
1
1
3
2
4
5
7
6
8
A
1
1
P
1
9
Byte
8
S
Address Rd
A
1
7
1
1
DATA_REQUEST
Write to TXBUF
EOM
1
Write to ACK
3
2
4
1
Byte
8
A
1
Byte
8
A
1
Byte
8
A
1
Byte
8
A
1
P
1
5
PMBus Slave Mode Command Examples
363
SNIU028A – February 2016 – Revised April 2016
Copyright © 2016, Texas Instruments Incorporated
PMBus Interface/I2C Interface
Figure 10-11. Simple Read of 4 Bytes with Full Automation
The steps are exactly the same as the sequence for 1 byte above, except that TX_COUNT needs to be 4
before TXBUF is written. Steps 6, 7, and 8 are the same for all reads, and will only be shown in the 1 byte
case to reduce complexity on the longer message sequence diagrams.
10.3.10 Simple Read of More than 4 Bytes with Full Automation
After the 4 byte TXBUF is emptied, there is a sequence for reloading it. Here is the diagram:
Figure 10-12. Simple Read of 5 Bytes with Full Automation
1. DATA_REQUEST is set t
DREQ1
nanoseconds after the falling edge of the clock for the last bit of the
address.
2. The firmware reads from PMBST, clearing the DATA_REQUEST bit. Since 4 bytes are being sent out,
the firmware needs to make sure that TX_COUNT is set to 4.
3. Next the firmware needs to write the bytes to TXBUF. All 4 bytes must be written in a single word write
operation. It takes t
txbwrite
ns after the write for any clock stretching of the ACK to be ended. If the
firmware is fast enough, no clock stretching will occur.
4. As soon as the data starts being transmitted, the TXBUF is transferred to the shift register
5. DATA_REQUEST is set t
DREQ1
nanoseconds after the falling edge of the clock for the last bit of the
fourth byte.
6. The firmware reads from PMBST, clearing the DATA_REQUEST bit. Since one byte is being sent out,