Rainbow Electronics MAX7359 - Manual (Page 13)

Only one autorepeat code is entered into the FIFO, regard-
less of the number of keys pressed. The autorepeat code
continues to be entered in the FIFO at the frequency set
by the bits D4–D1 until another key event is recorded.
Following the key-release event, if any keys are still
pressed, the MAX7359 restarts the autorepeat sequence.
Autosleep Register (0x06)
Autosleep puts the MAX7359 in sleep mode to draw minimal
current. When enabled, the MAX7359 enters sleep mode if
no keys are pressed for the autosleep time (Table 9).
Sleep Mode
In sleep mode, the MAX7359 draws minimal current.
Switch matrix current sources are turned off and pulled
up to V
CC . Writing a 0 to D7 in the configuration register
(0x01) puts the device in sleep mode. Writing a 1 to D7
or a key press, when the part is programmed to
autowake, can take the MAX7359 out of sleep mode.
Bit D7 in the configuration register gives the sleep
mode status and can be read anytime. The FIFO data
is maintained while in sleep mode.
Autowake
Key presses initiate autowake and the MAX7359 goes
into operating mode. Key presses that autowake the
MAX7359 are not lost. When a key is pressed while the
MAX7359 is in sleep mode, all analog circuitry, includ-
ing switch matrix current sources, turn on in 2ms. The
initial key needs to be pressed for 2ms plus the
debounce time to be stored in the FIFO. Autowakeup
can be disabled by writing a 0 to D1 in the configura-
tion register (0x01).
Serial Interface
Figure 1 shows the 2-wire serial interface timing details.
Serial Addressing
The MAX7359 operates as a slave that sends and
receives data through an I
2 C-compatible 2-wire inter-
face. The interface uses a serial-data line (SDA) and a
serial-clock line (SCL) to achieve bidirectional commu-
nication between master(s) and slave(s). A master (typ-
ically a microcontroller) initiates all data transfers to and
from the MAX7359 and generates the SCL clock that
synchronizes the data transfer.
The MAX7359’s SDA line operates as both an input and
an open-drain output. A pullup resistor, typically 4.7k
Ω,
is required on SDA. The MAX7359’s SCL line operates
only as an input. A pullup resistor is required on SCL if
there are multiple masters on the 2-wire interface, or if
the master in a single-master system has an open-drain
SCL output.
Each transmission consists of a START condition (Figure
2) sent by a master, followed by the MAX7359 7-bit slave
address plus R/
W bit, a register address byte, 1 or more
data bytes, and finally a STOP condition.
Start and Stop Conditions
Both SCL and SDA remain high when the interface is not
busy. A master signals the beginning of a transmission
with a START (S) condition by transitioning SDA from
high to low while SCL is high. When the master has fin-
ished communicating with the slave, it issues a STOP (P)
condition by transitioning SDA from low to high while SCL
is high. The bus is then free for another transmission.
Bit Transfer
One data bit is transferred during each clock pulse
(Figure 3). The data on SDA must remain stable while
SCL is high.
MAX7359
2-Wire Interfaced Low-EMI
Key Switch Controller/GPO
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REGISTER REGISTER DATA
RESERVED AUTOSHUTDOWN TIME
AUTOSLEEP REGISTER
D7 D6 D5 D4 D3 D2 D1 D0
No Autosleep 0 0 0 0 0 0 0 0
Autosleep for (ms)
8192 0 0 0 0 0 0 0 1
4096 0 0 0 0 0 0 1 0
2048 0 0 0 0 0 0 1 1
1024 0 0 0 0 0 1 0 0
512 0 0 0 0 0 1 0 1
256 0 0 0 0 0 1 1 0
256 0 0 0 0 0 1 1 1
Power-up default settings 0 0 0 0 0 1 1 1
Table 9. Autosleep Register Format (0x06)