LM8322JGR8X/NOPB National Semiconductor, LM8322JGR8X/NOPB Datasheet - Page 25

• Manufacturer Part Number: LM8322JGR8X/NOPB
• Description: IC MOBILE I/O COMPAN 36MICRARRAY
• Manufacturer: National Semiconductor

Specifications of LM8322JGR8X/NOPB

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM8322JGR8X

16.0 Host Interface
The two-wire ACCESS.bus interface is used to communicate
with a host. The ACCESS.bus interface is fully compliant with
the I
at 400 kHz (Fast mode).
All communication with the LM8322 over the ACCESS.bus
interface is initiated by the host, usually in response to an in-
terrupt request (IRQ low) asserted by the LM8322. The
LM8322 may request service from the host by asserting the
IRQ interrupt output.
16.1 START AND STOP CONDITIONS
Every transfer is preceded by a Start condition or a Repeated
Start condition. The latter occurs when a command follows
immediately upon another command without an intervening
Stop condition. A Stop condition indicates the end of trans-
mission. Every byte is acknowledged by the receiver.
16.2 CONTINUOUS COMMAND STRINGS
A host device may send a continuous string of commands
using the Repeated Start condition, which would block an-
other ACCESS.bus device from gaining control of the bus.
After Power-On the host device must send multiple com-
mands to initialize the LM8322 device. A minimal command
string will include the commands shown in Table 10.
A more comprehensive command string may include the ad-
ditional commands shown in Table 11.
WRITE_PORT_STATE Set port states of GPIO pins
WRITE_PORT_SEL
SET_KEY_SIZE
2
C bus standard. The LM8322 operates as a bus slave
WRITE_CFG
WRITE_CLK
READ_INT
Command
READ_ID
FIGURE 15. Start and Stop Conditions
TABLE 10. Minimal Command String
Read vendor ID and software
version
Check if NOINT bit is set in
interrupt register
Configure the LM8322
Set the size of the keypad
Set the clock mode for the PWM
unit
Set port direction for GPIO pins
Description
30013615
25
Note: Very long continuous command strings exceeding 30
milliseconds could overrun the ability of the LM8322 to pro-
cess commands if the time from the last clock cycle of a
command until the next Start condition or Repeated Start
condition is always shorter than 60 µs. A very long command
chain could prevent the LM8322 from performing any watch-
dog service and consequently could trigger a physical
RESET to the device.
To avoid overrunning the LM8322, the host should not send
a Start condition or a Repeated Start condition less than 100
µs after the last Stop condition or the last clock of a preceding
command.
16.3 DEVICE ADDRESS
The device address is controlled by states sampled on the
CONFIG_1 and CONFIG_2 pins, as shown in Table 12. In the
first byte of a bus transaction, a 7-bit address plus a direction
bit are broadcast by the bus master to all bus slaves.
If the CONFIG_1 and CONFIG_2 pins are left open, on-chip
pullups will select 1000 101X by default.
16.4 HOST WRITE COMMANDS
Some host commands include one or more data bytes written
to the LM8322. Figure 16 shows a SET_KEY_SIZE com-
mand, which consists of an address byte, a command byte,
and one data byte. The first byte is composed of a 7-bit slave
address in bits 7:1 and a direction bit in bit 0. The state of the
direction bit is 0 on writes from the host to the slave and 1 on
reads from the slave to the host.
The second byte sends the command. The SET_KEY_SIZE
command is 0x90.
The third byte send the data, in this case specifying the num-
ber of rows and columns for the keypad.
READ_PORT_STATE
CONFIG_1
SET_DEBOUNCE
SET_ACTIVE
READ_CFG
READ_CLK
Command
0
0
1
1
TABLE 12. Device Address Selection
TABLE 11. Additional Commands
CONFIG_2
0
1
0
1
Set debounce time
Set active time
Verify PWM clock settings
Verify configuration setting
Read all port states (physical levels
on pins)
Description
Device Address
1000 010X
1000 011X
1000 100X
1000 101X
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