AN2282

Hardware

5/19

1.2

EMI-ISA Interface

The CS8900A Ethernet controller includes a direct interface to the ISA bus. The ISA bus

(Industry Standard Architecture) has been the first standard in the IBM PC architecture;

detailed information and specification can be found in the following documents:

●

EISA Specification, Version 3.12. This document includes specifications for ISA as well

as the "Extended Industry Standard Architecture" that defines a 32-bit extension to the

ISA [2].

●

PS/2 Technical Reference - AT Bus Systems. This document includes signal definitions

and timing diagrams for the ISA bus used in some IBM computers [3].

At the same time, the CS8900A can be used for cost-effective, full-duplex Ethernet solutions

for non-ISA architectures as referenced in the application note AN83 from CIRRUS LOGIC®

Crystal LANTM CS8900A ETHERNET CONTROLLER TECHNICAL REFERENCE

MANUAL [4].

The reference schematic of the hardware interface between EMI and the ISA bus is shown

in Figure 2. The Chip Select 2 of EMI is used to address the Ethernet Controller; moreover

address line A23 of EMI is used together with CS.2 to enable read/write operations on

CS8900A. From a firmware point of view, this means that the Ethernet Controller is mapped

at base address 0x64800000; in this way the CS.2 is not committed only by the CS8900A

but it also can be used to address other devices.

Figure 2.

EMI-ISA glue logic reference schematic

The CS8900A can be accessed both in ISA IO mode and ISA memory mode; the glue logic

is designed to allow both access modes. The Address line A12 separates IO address space

and memory address space. When A12 is low the Ethernet Controller is accessed in IO

+3V3

+3V3

+3V3

nWR

GND

CS.2

QA12

QA11

QA10

QA9

QA8

QA7

+3.3V

GND

QA2

QA1

GND

QA0

QA3

+3.3V

GND

CS.2

IOR

A12

ME MR

ME MR

nAE

IOW

A12

ME MW

nWR

nA23

nRD

A0

A1

A4

A6

A8

A9

A10

A11

A3

A2

A5

A7

A12

nA23

WE0

WE1

nRD

ME MW

IOW

ME MR

IOR

QA4

QA5

QA6

CS.2

CS.2

D0

D1

D2

D3

D4

D5

D6

D7

D8

D9

D10

D11

D12

D13

D14

D15

U7

M7 4HC08TTR-TTSOP14

1

2

3

4

5

6

7

8

9

10

11

12

13

14

1

2

3

4

5

6

GND 8

9

10

11

12

13

VDD

IC5

74LVC32ATTR-TSSOP14

1

2

3

4

5

6

7

8

9

10

13

12

11

14

1A

1B

1Y

2A

2B

2Y

GND

3Y

3A

3B

4B

4A

4Y

vcc

IC100

74LVX573T

1

10

20

2

3

4

5

6

7

8

9

11

12

13

14

15

16

17

18

19

OE

GND

VCC

D0

D1

D2

D3

D4

D5

D6

D7

LE

Q7

Q6

Q5

Q4

Q3

Q2

Q1

Q0

IC6

74LVC32ATTR-TSSOP14

1

2

3

4

5

6

7

8

9

10

13

12

11

14

1A

1B

1Y

2A

2B

2Y

GND

3Y

3A

3B

4B

4A

4Y

vcc

U15

NOT

1

2

IC101

74LVX573T

1

10

20

2

3

4

5

6

7

8

9

11

12

13

14

15

16

17

18

19

OE

GND

VCC

D0

D1

D2

D3

D4

D5

D6

D7

LE

Q7

Q6

Q5

Q4

Q3

Q2

Q1

Q0

STR7 EMI Address Bus

STR7 EMI Control Bus

NIC ISA Control Bus

NIC ISA Address Bus

NIC nSBHE

STR7 EMI Data Bu s

NIC ISA Data Bus

NIC SA13 to SA19 , AEN,

CHIPSEL Grounded