Rainbow Electronics MAX16071 - Manual (Page 33)

12-Channel/8-Channel, Flash-Configurable System
Managers with Nonvolatile Fault Registers
MAX16070/MAX16071
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Packet Error Checking (PEC)
The MAX16070/MAX16071 feature a PEC mode that is
useful for improving the reliability of the communication
bus by detecting bit errors. By enabling PEC, an extra
CRC-8 error check byte is added in the data string dur-
ing each read and/or write sequence. Enable PEC by
writing a ‘1’ to r8Bh[7].
The CRC-8 byte is calculated using the polynomial
C = X
8 + X 2 + X + 1
The PEC calculation includes all bytes in the transmis-
sion, including address, command, and data. The PEC
calculation does not include ACK, NACK, START, STOP,
or REPEATED START.
Command Codes
The MAX16070/MAX16071 use eight command codes
for block read, block write, and other commands. See
Table 21 for a list of command codes.
To initiate a software reboot, send A7h using the send byte
format. A software-initiated reboot is functionally the same
as a hardware-initiated power-on reset. During boot-up,
flash configuration data in the range of 230h to 28Ch is
copied to r30h to r8Ch registers in the default page.
Send command code A8h to trigger a fault store to flash.
Configure the Critical Fault Log Control register (6Dh) to
store ADC conversion results and/or fault flags.
While in the flash page, send command code A9h to
access the flash page (addresses from 200h to 28Fh).
Once command code A9h has been sent, all addresses
are recognized as flash addresses only. Send command
code AAh to return to the default page (addresses from
000h to 0FFh). Send command code ABh to access
the user flash-page (addresses from 300h to 3A4h and
3ADh–3ffh), and send command code ACh to return to
the flash page.
Restrictions When Writing to Flash
Flash must be written to 8 bytes at a time. The initial
address must be aligned to 8-byte boundaries—the
three LSBs of the initial address must be ‘000.’ Write the
8 bytes using a single block-write command or using 8
successive Write Byte commands.
Send Byte
The send byte protocol allows the master device to send
one byte of data to the slave device (see Figure 11). The
send byte presets a register pointer address for a subse-
quent read or write. The slave sends a NACK instead of
an ACK if the master tries to send a memory address or
command code that is not allowed. If the master sends
A5h or A6h, the data is ACK, because this could be the
start of the write block or read block. If the master sends
a STOP condition before the slave asserts an ACK, the
internal address pointer does not change. If the master
sends A7h, this signifies a software reboot. The send
byte procedure is the following:
1) The master sends a START condition.
2) The master sends the 7-bit slave address and a write
bit (low).
3) The addressed slave asserts an ACK on SDA.
4) The master sends an 8-bit memory address or com-
mand code.
5) The addressed slave asserts an ACK (or NACK) on SDA.
6) The master sends a STOP condition.
Table 21. Command Codes
COMMAND
CODE
ACTION
A5h Block write
A6h Block read
A7h Reboot flash in register file
A8h Trigger emergency save to flash
A9h Flash page access ON
AAh Flash page access OFF
ABh User flash access ON (must be in flash page already)
ACh User flash access OFF (return to flash page)