COM20022I3V-HT datasheet(39/73 Pages) SMSC

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10 Mbps ARCNET (ANSI 878.1) Controller with 2Kx8 On-Chip RAM

Datasheet

SMSC COM20022I 3.3V Rev.C

Page 39

Revision 03-08-07

DATASHEET

Figure 6.1 -

Sequential Access Operation

6.3

Internal RAM

The integration of the 2K x 8 RAM in the COM20022I 3V represents significant real estate savings. The

most obvious benefit is the 48 pin package in which the device is now placed (a direct result of the

integration of RAM). In addition, the PC board is now free of the cumbersome external RAM, external

latch, and multiplexed address/data bus and control functions which were necessary to interface to the

RAM. The integration of RAM represents significant cost savings because it isolates the system designer

from the changing costs of external RAM and it minimizes reliability problems, assembly time and costs,

and layout complexity.

6.3.1

Sequential Access Memory

The internal RAM is accessed via a pointer-based scheme. Rather than interfering with system memory,

the internal RAM is indirectly accessed through the Address High and Low Pointer Registers. The data is

channeled to and from the microcontroller via the 8-bit data register. For example: a packet in the internal

RAM buffer is read by the microcontroller by writing the corresponding address into the Address Pointer

High and Low Registers (offsets 02H and 03H).

Note that the High Register should be written first,

followed by the Low Register, because writing to the Low Register loads the address. At this point the

device accesses that location and places the corresponding data into the data register.

The

microcontroller then reads the data register (offset 04H) to obtain the data at the specified location. If the

Auto Increment bit is set to logic "1", the device will automatically increment the address and place the

Address Pointer Register

Low

2K x 8

RAM

Data Register

I/O Address 04H

I/O Address 03H

11-Bit Counter

Memory

Address Bus

Memory

Data Bus

D0-D7

High

I/O Address 02H

INTERNAL

COM20022I3V-HT Datasheet(PDF) 39 Page - SMSC Corporation

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