LAN91C111 datasheet(54/125 Pages) MICROCHIP

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LAN91C111

DS00002276A-page 54

 2011-2016 Microchip Technology Inc.

COMMAND SEQUENCING

A second allocate command (command 1) should not be issued until the present one has completed. Completion is

determined by reading the FAILED bit of the allocation result register or through the allocation interrupt.

A second release command (commands 4, 5) should not be issued if the previous one is still being processed. The

BUSY bit indicates that a release command is in progress. After issuing command 5, the contents of the PNR should

not be changed until BUSY goes low. After issuing command 4, command 3 should not be issued until BUSY goes low.

BUSY BIT - Readable at bit 0 of the MMU command register address. When set indicates that MMU is still processing

a release command. When clear, MMU has already completed last release command. BUSY and FAILED bits are set

upon the trailing edge of command.

8.17

Bank 2 - Packet Number Register

PACKET NUMBER AT TX AREA - The value written into this register determines which packet number is accessible

through the TX area. Some MMU commands use the number stored in this register as the packet number parameter.

This register is cleared by a RESET or a RESET MMU Command.

This register is updated upon an ALLOCATE MEMORY MMU command.

FAILED - A zero indicates a successful allocation completion. If the allocation fails the bit is set and only cleared when

the pending allocation is satisfied. Defaults high upon reset and reset MMU command. For polling purposes, the

ALLOC_INT in the Interrupt Status Register should be used because it is synchronized to the read operation. Sequence:

Allocate Command

Poll ALLOC_INT bit until set

Read Allocation Result Register

ALLOCATED PACKET NUMBER - Packet number associated with the last memory allocation request. The value is only

valid if the FAILED bit is clear.

OFFSET

NAME

TYPE

SYMBOL

PACKET NUMBER

READ/WRITE

PNR

Reserved

PACKET NUMBER AT TX AREA

00000000

OFFSET

NAME

TYPE

SYMBOL

ALLOCATION RESULT

READ ONLY

ARR

FAILED

Reserved

ALLOCATED PACKET NUMBER

10000000

Note:

For software compatibility with future versions, the value read from the ARR after an allocation request is

intended to be written into the PNR as is, without masking higher bits (provided FAILED = 0).

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