GPBA01B datasheet(8/29 Pages) GENERALPLUS

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GPBA01B

Proprietary & Confidential

MAY 28, 2007

Version: 1.1

6.5. Daisy Chain

There are 11 pins connecting from MPU to BEX, except MC0, MC1,

and AD bus.

In addition, there is another pin, named CI, the

Cascade-In of BEX.

When CI goes from low to high, the VID/SID

of BEX will be reset and must be setup.

When accessing BEX,

the CI pin must keep in logical high level.

Both CI and CO provide the circuitry to concatenate up to seven

BEX.

In such case, the CO (Cascade-Out) of the former BEX is

connected to the CI of next BEX to form a daisy-chain.

After CI of

st BEX goes from low to high, the 1st setting of Volume ID, VID,

(setting $000DH) will apply to the 1

st BEX. After the 1st BEX is

configured, it will raise its CO.

The CO of the 1

BEX is

connected with the CI of the 2

nd BEX; as a result, the configuration

will apply to the 2

nd BEX, and…etc.

MC[1:0]

AD[7:0]

BEXA

OUT

MC[1:0]

AD[7:0]

MPU

MC[1:0]

AD[7:0]

BEXB

For correction operation, if there are 5 BEXs on the system, issue

exactly five unique VID.

After all VID have been set, any writing activity to $000D will be

taken as “selecting”.

For example, after setting the VID of the

BEXs as 1, 2, 3... up to 7, simply write 3 to $000DH to select and

access it when MPU intends to access BEX of ID 3.

Note that the sequence of ID is not necessary of 1, 2, 3...7.

The

user is allowed to set the IDs as 3, 2, 1... or 7,2,4... Just keep in

mind that the 1

st ID is applied to the 1st BEX in the daisy chain. The

0 is not a valid ID.

Because we want all BEXs to share the same BMI, every BEX

needs two variables, Volume-ID (VID) and Select-ID (SID) inside.

We must send unique VID to every BEX and then we should

choose one of these BEX by setting SID.

At any time, only one

BEX can operate

Which BEX will be activated depending on

which BEX has VID=SID (but VID cannot be 0).

$000DH register

is used for set both VID and SID, but VID can be written once only.

When MPU sends OUT=0, CI of BEXA=0 causes VID, SID, CO of

BEXA=0, too; CO of BEXA always causes VID, SID, CO of

BEXB=0.

Finally, all functions in these two GPBA01B are

disabled and all registers remain at the previous states, except

volume-id (VID) and select-id (SID), which are reset to zero.

6.5.1. Example

We will describe the action of two BEX on the daisy chain as

follows.

It’s important that MPU shares bus with BEXs.

How can

we identify BEX and send a unique VID to each BEX? It is

achieved by CI and CO.

MC[1:0]

AD[7:0]

BEXA

OUT

MC[1:0]

AD[7:0]

MPU

MC[1:0]

AD[7:0]

BEXB

VID =0

SID=0

VID =0

SID=0

$000DH

then acts as SID only.

VID are write-once register.

The first step

is accessing BEXA and then accessing BEXB as follows:

MPU’s OUT=0

MPU’s OUT=1

Send_addr_data($000d,$03)

; Set 3 to VID of BEXA(VID write once)

Send_addr_data($000d,$05)

; Set 5 to VID of BEXB(VID write once)

Send_addr_data($000d,$03)

; Set 3 to SID of BEXA and BEXB

(BEXA active, BEXB inactive)

Send_addr_data($0023,$XX)

; Configure BEXA as ‘Memory extender’ or ‘I/O extender’

(Access BEXA….)

…..

Send_addr_data($000d,$05)

; Set 5 to SID of BEXA and BEXB

(BEXA inactive, BEXB active)

10. Send_addr_data($0023,$XX)

; Configure BEXB as ‘Memory extender’ or ‘I/O extender’

11. (Access BEXB…..)

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