LAN91C111 Datasheet, PDF (54/125 Pages) SMSC Corporation – 10/100 Non-PCI Ethernet Single Chip MAC + PHY

LAN91C111
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
OFFSET
2
NAME
PACKET NUMBER
REGISTER
TYPE
SYMBOL
READ/WRITE
PNR
Reserved Reserved
PACKET NUMBER AT TX AREA
0
0
0
0
0
0
0
0
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.
OFFSET
3
NAME
ALLOCATION RESULT
REGISTER
TYPE
READ ONLY
This register is updated upon an ALLOCATE MEMORY MMU command.
SYMBOL
ARR
FAILED
Reserved
ALLOCATED PACKET NUMBER
1
0
0
0
0
0
0
0
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:
1. Allocate Command
2. Poll ALLOC_INT bit until set
3. 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.
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).
DS00002276A-page 54
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