MAX7359 Maxim, MAX7359 Datasheet - Page 16

• Manufacturer Part Number: MAX7359
• Description: The MAX7359 I²C interfaced peripheral provides microprocessors with management of up to 64 key switches
• Manufacturer: Maxim

2-Wire Interfaced Low-EMI
Key Switch Controller/GPO
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).
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
Figure 6. Command Byte Received
Figure 7. Command and Single Data Byte Received
16
S
______________________________________________________________________________________
Message Format for Reading the
SLAVE ADDRESS
Message Format for Writing the
ACKNOWLEDGE FROM MAX7359
S
COMMAND BYTE IS STORED ON RECEIPT OF
ACKNOWLEDGE FROM MAX7359
R/W
Key-Scan Controller
Key-Scan Controller
SLAVE ADDRESS
0
ACKNOWLEDGE CONDITION
A
D7
R/W
D6
D5
0
ACKNOWLEDGE FROM MAX7359
COMMAND BYTE
D4
A
D3
D7
D2
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).
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.
Table 11. Autoincrement Rules
Keys FIFO
Autoshutdown
All other
D6
REGISTER
FUNCTION
D1
ACKNOWLEDGE FROM MAX7359
D5
COMMAND BYTE
D0
D4
A
D3
Operation with Multiple Masters
D7
0x00
0x06
0x01 thru 0x05
CODE (hex)
D2
ADDRESS
D6
D1
D5
ACKNOWLEDGE FROM MAX7359
D0
D4
DATA BYTE
1 BYTE
A
0x00
0x00
Addr + 0x01
D3
P
AUTOINCREMENT
D2
ADDRESS (hex)
COMMAND BYTE ADDRESS
D1
AUTOINCREMENT
D0
A
P