DP83916 datasheet(23/96 Pages) NSC

23 / 96 page

40 SONIC-16 Registers (Continued)

TLF11722 – 21

FIGURE 4-1 CAM Organization

the SONIC-16 is in software reset The CDA resides in the

same 64k byte block of memory as the Receive Resource

Area (RRA) and contains descriptors for loading the CAM

registers These descriptors are contiguous and each de-

scriptor consists of four 16-bit fields

(Figure 4-2) The first

field contains the value to be loaded into the CAM Entry

Pointer and the remaining fields are for the three CAM Ad-

dress Ports (see Section 4310) In addition there is one

more field after the last descriptor containing the mask for

the CAM Enable register Each of the CAM descriptors are

addressed by the CAM Descriptor Pointer (CDP) register

After the system has initialized the CDA it can issue the

Load CAM command to program the SONIC-16 to read the

CDA and load the CAM The procedure for issuing the Load

CAM command is as follows

1 Initialize the Upper Receive Resource Address (URRA)

within the same 64k page as the Receive Resource

Area (See Section 439)

2 Initialize the CDA as described above

3 Initialize the CAM Descriptor Count with the number of

CAM descriptors Note only the lower 5 bits are used in

this register The other bits are don’t cares (See Section

4310)

4 Initialize the CAM Descriptor Pointer to locate the first

descriptor in the CDA This register must be reloaded

each time a new Load CAM command is issued

5 Issue the Load CAM command (LCAM) in the Command

If a transmission or reception is in progress the CAM DMA

function will not occur until these operations are complete

When the SONIC-16 completes the Load CAM command

the CDP register points to the next location after the CAM

Enable field and the CDC equals zero The SONIC-16 resets

the LCAM bit in the Command register and sets the Load

CAM Done (LCD) bit in the ISR

TLF11722 – 22

FIGURE 4-2 CAM Descriptor Area Format

DP83916 Datasheet(PDF) 23 Page - National Semiconductor (TI)