Maxim Integrated 18-7
MAX31782 User’s Guide
Revision 0; 8/11
4) Possibly poll returned data until command execution completes.
5) Transmit 00h on TDI for each Data Out byte. Read the Data Out byte on TDO.
6) Transmit 00h on TDI and verify that the Return byte output on TDO is 3Eh.
7) The Dummy RX byte is not required for the JTAG bootloader to operate.
Some of the bootloader commands, such as the erase and CRC commands require extra time to execute. For these
commands, the two status bits can be used to verify the state of the bootloader. After issuing any of these commands,
the NOP command can continuously be sent to the bootloader. If the returned status bits are 10, the bootloader is still
busy processing the command. If the status bits are 11, the bootloader has completed execution of the command. The
first byte that was returned with status bits 11 is the first byte of valid returned data from the bootloader.
18.2.2 I
2
C Bootloader Protocol
After entering the I
2
C bootloader, all I
2
C communication takes place on the default I
2
C slave address 36h. When writ-
ing data to the MAX31782, slave address 36h (R/W
bit = 0) is used. To read data from the MAX31782 I
2
C bootloader,
slave address 37h (R/W
bit = 1) is used. The I
2
C bootloader does not return the status bits that are available from the
JTAG bootloader. The following I
2
C steps are required to send each command
1) Send an I
2
C START, followed by writing slave address 36h (R/W bit set to write).
2) Write command byte.
3) Write any Data In bytes.
4) The NOP byte is not required for the I
2
C interface. Sending a NOP byte when using the I
2
C bootloader places the
bootloader into an unknown state. Instead, an I
2
C restart needs to be issued, followed by writing slave address 37h
(R/W
bit set to read).
5) Possibly poll returned data until command execution completes.
6) Read and ACK all Data Out bytes.
7) Read and ACK the Return byte, verify that 3Eh was returned.
8) Read and NACK the Dummy RX byte. Ignore the returned data.
9) Send an I
2
C STOP.
Some of the bootloader commands such as the erase and CRC commands require extra time to execute. For these
commands, the I
2
C port can be continuously polled to determine when the command completes. This polling is done
by reading the returned data bytes after sending slave address 37h. The I
2
C bootloader returns data B7h while it is
currently busy. When data other than B7h is returned, the bootloader is returning valid data. An example of polling for
the CRC Code command is shown in Figure 18-2. After sending slave address 37h, the I
2
C bootloader outputs B7h until
the command has finished execution. The I
2
C master needs to continue reading and returning ACK’s until a string of
four bytes with values B7h, YYh, ZZh, 3Eh is returned. The master then reads the Dummy RX byte and NACKs this byte.
Figure 18-2. I
2
C Bootloader Polling
SLAVE ADDRESS (W)
36h
COMMAND
30h
S A
DATA IN
02h
A
Data In AddrL
00h
A
Data In AddrH
00h
A
Data In LengthL
00h
A
Data In LengthH
01h
A A
SLAVE ADDRESS (R)
37h
POLLING
B7h
Sr A
POLLING...
B7h
A
POLLING
B7h
A
DATA OUT CRCL
YYh
A
DATA OUT CRCH
ZZh
A
RETURN
3Eh
A
A
DUMMY RX
XX
NA P
S = START A = ACKNOWLEDGE
Sr = REPEATED START NA = NOT ACKNOWLEDGE
P = STOP SHADED = SLAVE TRANSACTION
KEY
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