LAN91C111 datasheet(56/125 Pages) MICROCHIP

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LAN91C111

DS00002276A-page 56

 2011-2016 Microchip Technology Inc.

8.19

Bank 2 - Pointer Register

POINTER REGISTER - The value of this register determines the address to be accessed within the transmit or receive

areas. It will auto-increment on accesses to the data register when AUTO INCR. is set. The increment is by one for every

byte access, by two for every word access, and by four for every double word access. When RCV is set the address

refers to the receive area and uses the output of RX FIFO as the packet number, when RCV is clear the address refers

to the transmit area and uses the packet number at the Packet Number Register.

READ - Determines the type of access to follow. If the READ bit is high the operation intended is a read. If the READ

bit is low the operation is a write. Loading a new pointer value, with the READ bit high, generates a pre-fetch into the

Data Register for read purposes.

Readback of the pointer will indicate the value of the address last accessed by the CPU (rather than the last pre-

fetched). This allows any interrupt routine that uses the pointer, to save it and restore it without affecting the process

being interrupted. The Pointer Register should not be loaded until the Data Register FIFO is empty. The NOT EMPTY

bit of this register can be read to determine if the FIFO is empty. On reads, if ARDY is not connected to the host, the

Data Register should not be read before 370ns after the pointer was loaded to allow the Data Register FIFO to fill.

If the pointer is loaded using 8 bit writes, the low byte should be loaded first and the high byte last.

Reserved - Must be 0

NOT EMPTY - When set indicates that the Write Data FIFO is not empty yet. The CPU can verify that the FIFO is empty

before loading a new pointer value. This is a read only bit.

OFFSET

NAME

TYPE

SYMBOL

POINTER REGISTER

READ/WRITE

NOT EMPTY IS

A READ ONLY

BIT

PTR

HIGH

BYTE

RCV

AUTO

INCR.

READ

Reserved

NOT

EMPTY

POINTER HIGH

000

LOW

BYTE

POINTER LOW

000

Note:

If AUTO INCR. is not set, the pointer must be loaded with a dword aligned value.

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