Pixelink PL-A780 System Manual Download

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Developing Software for the PL-A780

Document No.: 04646-01

PixeLINK PL-A780

MACHINE VISION CAMERA

SYSTEM GUIDE

6.3 How Do 1394 Devices Communicate?

Essentially the IEEE - 1394 FireWire bus uses a memory mapped communication protocol.
1394 transactions can be considered to be a read or write of data to a specified memory
address. 1394 uses 64bits of addressing: 16 bits for bus and node addressing with each
node (or device) on the bus having 48 bits of address space. The IIDC specification defines
how the address space on an IIDC compliant camera is implemented.

NOTE:

1394 uses big-endian notation, that means that the most significant byte comes first

and the most significant bit is bit 0. The PC uses little endian notation, where the least
significant byte comes first.

6.4 Communication With a IIDC Camera

In order to begin communication with an IIDC camera it is first necessary to determine in
which portion of the address space the IIDC camera is located. To allow flexibility in device
implementation the IIDC address space is not the same between devices but can be selected
by the camera manufacturer.

The IIDC specification defines the base address of the IIDC address space as

FFFF Fxxx xxxh

where the

xxx xxxxh

is determined from the camera’s

Configuration ROM

6.4.1 Navigating the Configuration ROM

The IIDC specification defines the format of the

Configuration ROM

for IIDC cameras. The

offsets listed in the

Root Directory

table are all relative to the base address

FFFF F000

0000h

To determine the location of the

Unit Directory

the

unit_directory_offset

field must be read

from offset

0424h

(or address

FFFF F000 0424h

). This field consists of an identifying key

and a relative

quadlet offset

. The identifying key is an 8 bit value that for the unit directory

offset is

D1h

. So if the value in the

unit_directory_offset

field is

D100 0004h

then the offset

for the

unit directory

is 0424h + 4*04h =

0434h

(or address

FFFF F000 0434h

To determine the location of the Unit Dependent Directory the

unit_dependent_directory_offset

field must be read from offset

000Ch

of the

Unit Directory

(or address

FFFF F000 0440h

using the above example unit directory offset). The identifying

key for the unit dependent directory offset is

D4h

. So if the value in the

unit_dependent_directory_offset

field is

D400 0001h

then the offset for the unit dependent

directory is 0440h + 04h =

0444h

(or address

FFFF F000 0444h

The Unit Dependent Directory contains, among other things, the

IIDC Base Address

, which

can be read from the

command_regs_base

field of the Unit Dependent Directory. The

identifying key for the

command_regs_base

field is

40h

. So if the value of that field is

4034

0000h

then the offset of the IIDC address space is

00D0 0000h

or the

IIDC Base Address

FFFF F0D0 0000h

NOTE:

This sample

IIDC Base Address

will be used in all further examples in this document.

6.4.2 IIDC Command Registers

In Section 1 of the IIDC specification all Command registers (or CSRs) are defined. The
offsets for all of these registers, unless otherwise specified, are relative to the

IIDC Base

Address

. The IIDC CSRs consist of Inquiry Registers and Control Registers. The IIDC

specification is designed to support many different types of cameras with many different
features, the Inquiry registers are used by controlling software to determine which of these