Using Boot Rom Pmbus Interface - Texas Instruments UCD3138 Technical Reference Manual

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13.1.5 Using BOOT ROM PMBus Interface

If the neither checksum matches, the Boot ROM retains control of the processor. The Boot ROM
configures the chip as a PMBus Slave, so the host needs to act as a PMBus Master. The Boot ROM is
always at address 11 (0x0B). It provides a set of PMBus commands which can be used to control and
program the UCD3138.
These commands are:
The read and write message names are selected to avoid confusion with the Write Word and Block Write
messages in the PMBus Specification.
13.2 Memory Read Functionality
A total of 4 PMBus command bytes have been assigned for read functionality in the UCD3138 Boot ROM.
3 of these messages utilize a read format, in which the PMBus Master provides an address and command
byte to the UCD3138 and expects read data returned by the slave. These commands make it possible to
read from any valid memory location. They can be used to read from peripheral registers as well as from
memories.
13.2.1 Configure Read Address
Since the read commands only provide a command code, it is first necessary to provide an address to
read from. The read address is set up through a PMBus Write Block message with a command byte of
0xFD. Starting with the device address of 0xB (with R/W bit set low), the Configure Read Address
message contains a command byte of 0xFD, followed by 5 data bytes and a PEC byte. The first data byte
represents the block size for a PMBus Block Write message, which will always contain a value of 0x4 for
this message type. The remaining bytes represent the read address, starting with the most significant byte
in the second data byte and the least significant byte in the fifth data byte. The PEC byte completes the
message. The PMBus Master provides all 8 bytes of the message.
Note that the device address occupies bits 7 to 1 of the second byte, and the R/W bit occupies bit 0. So
with a device address of 0xB and the R/W bit = 0, the byte value will be 0x16. See
more details.
Also note that in the following illustrations, grey boxes indicate communications from master to slave
(UCD) and white boxes communications from UCD to master.
Start Device Address & R/W
Read Address[24:16]
SNIU028A – February 2016 – Revised April 2016
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Boot ROM Function
Configure Read Address
Read 4 Bytes
Read 16 Bytes
Read Next 16 Bytes
Write 4 Bytes
Write 16 Bytes
Write Next 16 Bytes
Mass Erase Flash
Page Erase Flash
Execute from Program Flash
Calculate Checksum
Read Checksum
Read Version
Command Byte (0xFD)
(0x16)
Read Address[15:8] Read Address[7:0]
Copyright © 2016, Texas Instruments Incorporated
Command Byte
0xFD
0xFA
0xF9
0xF8
0xF5
0xF4
0xF3
0xF2
0xF1
0xF0
0xEF
0xEE
0xEC
Section 10.10.1
Block Size (0x04)
PEC
Boot ROM and Boot Flash
Boot ROM Function
for
Read Address[31:24]
Stop
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