TNETA1575 datasheet(17/45 Pages) TI1

17 / 45 page

TNETA1575

ATM SEGMENTATION AND REASSEMBLY DEVICE

WITH PCI-HOST AND COPROCESSOR INTERFACES

SDNS040C – MAY 1996 – REVISED JUNE 1998

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

control-memory interface (continued)

The SAR control-memory port is used to select both the external SRAM that stores the local-data structures

and state information for the TNETA1575 and an external device that can be used to provide an external

scheduler and other transmit data structures. The total control-memory address space consists of 128K

locations, with 64K locations dedicated to the TNETA1575 SRAM, and the remaining 64K dedicated to an

external device such as an external scheduler (see Figure 3).

Control SRAM

64K

× 32

CMSELLO = low, CMSELHI = high

External Device

64K

× 32

CMSELLO = high, CMSELHI = low

Figure 3. Control-Memory Address Space

Control memory select bit CMSELHI is used to select the upper 64K-address space. CMSELHI is active low

when the higher 64K addresses are selected, and inactive when the lower 64K addresses are selected. The

control-memory select bit CMSELLO is used to select the lower 64K-address space.

In addition, when the CMSELLO terminal is active low and the lower 64K addresses are selected, the user can

select between a single 64K

× 32 SRAM bank or two 32K × 32 SRAM banks. The two terminals CMSB1 and

CMSB2 are active low and allow the user to select between the two banks, as follows:

CMSELLO is active low and CMA15 is low to select bank 1 (CMSB1 is enabled).

CMSELLO is active low and CMA15 is high to select bank 2 (CMSB2 is enabled).

There are 16 control-memory address terminals that are used to address the various blocks of control memory.

Together with the two select terminal (CMSELLO and CMSELHI) and the two bank operating terminals, these

20 terminals provide for a total of 128K addressable-memory locations.

CONTROL-MEMORY

ADDRESS SPACE SELECTED

(HEXADECIMAL)

CMSELLO

CMSB1

CMSB2

CMSELHI

00000–07FFF

08000–0FFFF

10000–1FFFF

TNETA1575 数据表(PDF) 17 Page - Texas Instruments

TNETA1575 数据表(HTML) 17 Page - Texas Instruments

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

数据表下载