STLC5465B datasheet(38/101 Pages) STMICROELECTRONICS

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III.5 - Memory Interface

III.5.1 - Function Description

The memory interface allows the connection of

Static or Dynamic RAM. The memory space ad-

dressable in the two configurationsis not the same.

In the case of dynamic memory (DRAM), the mem-

ory interface will address up to 16 Megabytes. In

case of staticmemory (SRAM) only 1 Megabytewill

be addressed. The memory location is always or-

ganized in 16 bits.

The memory is shared between the

Multi-HDLC

and the microprocessor. The access to the memory

is arbitrated by an internal function of the circuit:

the bus arbitration.

III.5.2 - Choice of memory versus microproc-

essor and capacity required

The memory interface depends on the memory

chips which are connected. As the memory chips

will be chosen versus the microprocessor and the

wanted memory space, the following table pre-

sents the different configurations DRAM and

SRAM selection versus

µP.

Example 1 : if the applicationrequires 16 bit mProc-

essor and 1 Megaword Shared memory size, three

capabilities are offered :

- 4 DRAM Circuits (256Kx16) or

- 4 DRAM Circuits (1Mx4) or

- 1 DRAM Circuit (1Mx16).

Example 2 : if the application requires 8 bit mProc-

essor and 1 Megabyte Shared memory size, three

capabilities are offered:

- 2 DRAM Circuits (256Kx16) or

- 8 SRAM Circuits (128Kx8) or

- 2 SRAM Circuits (512kx8).

Example 3 : for small applications it is possible to

connect 2 SRAM Circuits (128Kx8) to obtain 256

Kilobytes shared memory.

III.5.3 - Memory Cycle

For SRAM and DRAM, the different cycles are

programmable. See Memory Interface Configura-

tion Regist. MICR (32)H on Page 88.

Each cycle is equal to : p x 1/f

with f the frequencyof signal applied to the Crystal

1 input and p selected by the user. See page 9.

III - FUNCTIONAL DESCRIPTION (continued)

Table 22 : DRAM and SDRAM Selection versus

µP

Microprocessor and

shared memory

Shared memory size required by the application

8 bits

µProcessor

Number of

Megabytes

0.5

16/32 bits

µProcessor

Number of

Megawords

0.25

0.5

DRAM Circuits proposed

Capacity

Organization

4 Megabits

256Kx16

1(256Kx16)

2(256Kx16)

4(256Kx16)

1Mx4

4(1Mx4)

8(1Mx4)

16(1Mx4)

16 Megabits

1Mx16

1(1Mx16)

2(1Mx16)

4(1Mx16)

4Mx4

4(4Mx4)

8(4Mx4)

64 Megabits

4Mx16

1(4Mx16)

2(4Mx16)

SRAM Circuits proposed

Not possible

Capacity

Organization

1 Megabits

128Kx8

4(128Kx8)

8(128Kx8)

4 Megabits

512kx8

2(512kx8)

STLC5465B

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