Maxim Integrated MAX31782 - Manual (Page 157)

  MaximIntegrated  18-6
MAX31782 User’s Guide
Revision 0; 8/11
18.1.4I 2 CSystemProgrammingBufferRegister(I2C�SPB)
Table18-4.ExampleBootloadCommand
18.2.1JTAGBootloaderProtocol
The JTAG port consists of a shift register . As data is clocked into TDI, data is clocked out of TDO . Each “byte” on the
JTAG port is actually 10 bits . The two least significant bits are the status bits described in
Table 18-2 . The data that is
input to the device on the TDI pin should have the two status bits set to 0 . The following steps are required for each
command .
1) Transmit the Command byte on TDI . Ignore the returned data on TDO .
2) Transmit any Data In bytes on TDI . Ignore the returned data on TDO .
3) Transmit the NOP byte of 00h, on TDI . Ignore the returned data on TDO .
18.2BootloaderOperation
Once in bootloader mode, the JTAG and I 2 C interfaces both use the same commands . How these commands are
implemented will be different between the two interfaces . Table 18-4 shows an example command and parameters . The
next two sections detail how to implement these commands using either the JTAG or I 2 C interface .
Byte(s) Command DataIn NOP DataOut Return DummyRX
Input Command Data In 00h 00h 00h 00h
Output X X X Data Out 3Eh X
BYTENAME DESCRIPTION
Command
All bootloader commands begin with a single command byte . The upper four bits of this command byte define
the command family (from 0 to 15) and the lower four bits define the specific command within that family .
Data In
Data bytes that are input to the bootloader that are required for the command . The number of Data In bytes var-
ies for each command . Some commands do not require any Data In bytes .
NOP The NOP byte is only used for JTAG mode . This is a byte of 00h that is clocked into TDI, while TDO is ignored .
Data Out
Data Out is any data that is returned by the bootloader . The number of Data Out bytes varies for each com-
mand . Some commands do not output any Data Out bytes .
Return
A return value of 3Eh is output by the bootloader following the successful completion of a command . If the
Return byte is read prior to 3Eh being loaded by the bootloader, the read will return the data that is currently
in the shift register . The value 3Eh is only loaded into the shift register once . Any subsequent reads will return
invalid data . In JTAG bootload mode, status bits will tell when ROM loader is sending valid 3Eh .
Dummy RX The Dummy RX byte is only required for I 2 C mode . This is a dummy read of one byte, followed by a NACK .
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Name — —
— —
— —
— — — — — —
—
— —
I2C_SPE
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Access r r r r r r r r r r r r r r r rw
BIT NAME DESCRIPTION
15:1 — Reserved . The user should not write to these bits .
0 I2C_SPE
Setting this bit to a 1, by writing to slave address 34h, denotes that I 2 C bootloading is desired upon
exiting reset . The logic state of I2C_SPE is examined by the utility ROM following a reset to determine
the program flow . When I2C_SPE = 1, the I
2 C bootstrap loader is activated to perform a bootstrap
loader function . Also, if the MAX31782 does not contain a valid password, this bit is set during reset,
followed by entry into the I
2 C bootstrap loader .