ENC424J600 datasheet(36/168 Pages) MICROCHIP

36 / 168 page

ENC424J600/624J600

DS39935C-page 34

 2010 Microchip Technology Inc.

3.5.5

INDIRECT SRAM BUFFER ACCESS

Indirect access to the SRAM buffer is available to all I/O

interfaces. For the SPI interface, it is the only method

available. For PSP interfaces, it may be used in

addition to the direct access method.

Three separate pointer pairs are available for the host

microcontroller to use when accessing the SRAM:

• General Purpose Buffer Read/Write Pointer

(EGPRDPT/EGPWRPT)

• Receive Buffer Read/Write Pointer

(ERXRDPT/ERXWRPT)

• User-Defined Area Read/Write Pointer

(EUDARDPT/EUDAWRPT)

Each of these pointer pairs provides an 8-bit virtual

window register (EGPDATA, ERXDATA and EUDATA)

through which the SRAM data is read or written. The

pointers and their associated data windows are shown

in Figure 3-5.

EGPDATA, ERXDATA and EUDADATA are all 8 bits

wide. When writing to them using a 16-bit PSP

interface, the low-order byte select or write enable must

be used; strobing the high byte Byte Select or Write

Enable has no effect. When reading from a 16-bit PSP

interface, one byte of useful data will be returned on the

lower 8 bits of the data bus; the upper 8 bits are to be

ignored.

When a data window register is read, the memory

contents at the address indicated by the corresponding

Read Pointer are obtained and presented to the host

microcontroller. Similarly, when a data window register

is written, the memory contents at the address

indicated by the corresponding Write Pointer are

updated by the data from the host microcontroller.

Following a read/write operation, the appropriate

pointer is automatically incremented in hardware.

FIGURE 3-5:

POINTERS FOR INDIRECT BUFFER ACCESS

General Purpose

Buffer

0000h

5FFFh

Circular RX FIFO

Buffer

ERXST

ERXST – 1

EGPRDPT

EGPWRPT

ERXRDPT

ERXWRPT

EUDARDPT

EUDAWRPT

EUDAST

EUDAND

EGPDATA

ERXDATA

EUDADATA

EGPDATA

ERXDATA

EUDADATA

EGPDATA

ERXDATA

Unimplemented

Read

Write

Read

Write

Read

Write

Data Windows

Buffer Pointers

ENC424J600 Datasheet(PDF) 36 Page - Microchip Technology

ENC424J600 Datasheet(HTML) 36 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL