Register Format •• 15
3
Register Format
In this chapter, a primitive digital I/O operations of 725x prodcuts will
be specified. The I/O operations are also included.
3.1 I/O Port Base Address
The PCI-7250 or cPCI-7252 functions as a 32-bit PCI target device to
any master on the PCI bus. There are three types of registers on the
PCI-725X: PCI Configuration Registers (PCR), Local Configuration
Registers (LCR) and PCI-725X registers.
The PCR which conforms the PCI-bus specifications is initialized and
controlled by the system plug & play PCI BIOS. Please refer to the PCI
BIOS specification to understand how to get information from the
PCRs.
The LCR is specified by the PCI bus controller PLX-9050. It is not
necessary for users to understand the details of the LCR if you use the
software library. The base address of the LCR is assigned by the PCI
p&p BIOS. The assigned address is located at offset 14h of PCR.
Please refer to the PCI-9050’s data sheet for the detail operation of the
LCR and also the register format of the PCR.
The PCI-725X registers are shown in the Table 3.1. The base address
of the PCI-725X registers is also assigned by the PCI p&p BIOS. The
assigned base address is located at offset 18h of PCR. Therefore,
users can read the PCR to know the base address by using the BIOS
function call. Note that the PCI-725X registers are all 16 bits. The
users can access these registers by 16 bits I/O instructions.
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