Rainbow Electronics MAX7359 - Manual (Page 16)

MAX7359
2-Wire Interfaced Low-EMI
Key Switch Controller/GPO
16 ______________________________________________________________________________________
S A A P 0 SLAVE ADDRESS COMMAND BYTE
D7 D6 D5 D4 D3 D2 D1 D0
COMMAND BYTE IS STORED ON RECEIPT OF
ACKNOWLEDGE CONDITION
ACKNOWLEDGE FROM MAX7359
ACKNOWLEDGE FROM MAX7359
R/W
Figure 6. Command Byte Received
S A A A P 0 SLAVE ADDRESS COMMAND BYTE DATA BYTE
1 BYTE
AUTOINCREMENT
COMMAND BYTE ADDRESS
D7 D6 D5 D4 D3 D2 D1 D0 D1 D0 D3 D2 D5 D4 D7 D6
ACKNOWLEDGE FROM MAX7359 ACKNOWLEDGE FROM MAX7359
ACKNOWLEDGE FROM MAX7359
R/W
Figure 7. Command and Single Data Byte Received
MAX7359
Message Format for Writing the
Key-Scan Controller
A write to the MAX7359 comprises the transmission of the
slave address with the R/
W bit set to zero, followed by at
least 1 byte of information. The first byte of information is
the command byte. The command byte determines which
register of the MAX7359 is to be written by the next byte,
if received. If a STOP condition is detected after the com-
mand byte is received, the MAX7359 takes no further
action (Figure 6) beyond storing the command byte.
Any bytes received after the command byte are data
bytes. The first data byte goes into the internal register of
the MAX7359 selected by the command byte (Figure 7).
If multiple data bytes are transmitted before a STOP
condition is detected, these bytes are generally stored
in subsequent MAX7359 internal registers (Table 7)
because the command byte address generally autoin-
crements (Table 11).
Message Format for Reading the
Key-Scan Controller
The MAX7359 is read using the MAX7359’s internally
stored command byte as an address pointer, the same
way the stored command byte is used as an address
pointer for a write. The pointer generally autoincrements
after each data byte is read using the same rules as for
a write (Table 11). Thus, a read is initiated by first con-
figuring the MAX7359’s command byte by performing a
write (Figure 6). The master can now read n consecu-
tive bytes from the MAX7359, with the first data byte
being read from the register addressed by the initial-
ized command byte. When performing read-after-write
verification, remember to reset the command byte’s
address because the stored command byte address is
generally autoincremented after the write (Figure 8,
Table 11).
Operation with Multiple Masters
If the MAX7359 is operated on a 2-wire interface with mul-
tiple masters, a master reading the MAX7359 should use
a repeated start between the write that sets the
MAX7359’s address pointer, and the read(s) that takes
the data from the location(s). This is because it is possible
for master 2 to take over the bus after master 1 has set up
the MAX7359’s address pointer but before master 1 has
read the data. If master 2 subsequently resets the
MAX7359’s address pointer, master 1’s read may be from
an unexpected location.
REGISTER
FUNCTION
ADDRESS
CODE (hex)
AUTOINCREMENT
ADDRESS (hex)
Keys FIFO 0x00 0x00
Autoshutdown 0x06 0x00
All other 0x01 thru 0x05 Addr + 0x01
Table 11. Autoincrement Rules