Digi NS9750 User Manual

Page 570

I 2 C c o m m a n d i n t e r f a c e

5 4 6

N S 9 7 5 0 H a r d w a r e R e f e r e n c e

Locked interrupt driven mode

C operates in a locked interrupt driven mode, which means that each command

issued must wait for an interrupt response before the next command can be issued
(illustrated in "Flow charts," beginning on page 556).

The first bit of the command — 0 or 1 — indicates to which module — master or slave,
respectively — the command in the CMD field (of the

CMD_TX_DATA_REG

; see page 548)

is sent. The master module can be sent a master command only; the slave module
can be sent a slave command only (see "Master and slave module commands,"
beginning on page 546, for a list of commands). If a command is sent to the master
module, that module is locked until a command acknowledgement is given. Similarly,
if a command is sent to the slave module, the slave module is locked until it receives
a command acknowledgement. With either module, the acknowledgement can be any
interrupt associated with that module. When a module is locked, another command
must not be sent to that module.

The command lock status can be checked in the

STATUS_RX_DATA_REG

Master module and slave module commands

The I

C master recognizes four high-level commands, which are used in the CMD field

of the Command register (see page 548); the I

C slave recognizes two high-level

commands:

Command

Name

Description

hex

M_NOP

No operation.

hex

M_READ

Start reading bytes from slave.

hex

M_WRITE

Start writing bytes to slave.

hex

M_STOP

Stop this transaction (give up the I

C bus).

hex

S_NOP

No operation. This command is necessary for 16-bit
mode, providing data in

TX_DATA_REG

without a

command.

hex

S_STOP

Stop transaction by not acknowledging the byte
received.

Table 335: Master and slave module commands