SB4002A_Data Sheet_EN

SB4002A

3.3 Data Split and Combine

SB4002A supports the data path in BYTE, WORD and DWORD on the Legacy bus depending on

the characteristics of the device. The PCI bus data path is based on DWORD, and access in byte

and word is also available. If the supported data path type is not consistent between the PCI bus

access and the Legacy bus device - e.g., the PCI bus access is DWORD or WORD, while the

Legacy bus device is a BYTE device; or the PCI bus access is DWORD, while the Legacy bus

device is a WORD device - the PCI bus can terminate the transaction with Target Abort. SB4002A,

however, adopts the concept of Data Split and Combine to complete the transaction in the above

case. This concept is applied to the delayed access only.

For the write process, the device stores the data in FIFO, and when the Legacy bus starts the write

access, starts burst access to the bandwidth of the Legacy bus device. For example, if the Legacy

bus device is a BYTE device, and a DWORD data is stored in FIFO, the Legacy bus device

executes access 4 times by dividing the data into 4 sets of BYTE data.

For the read process, the device executes burst access to the data path of the Legacy bus device,

and stores the data in FIFO. For example, if the Legacy bus device is a BYTE device, the Legacy

bus device executes BYTE access 4 times, stores a set of DWORD data, and transmits the data

when the PCI bus starts a transaction.

TRDY#

ADD+2ADD

IOW#

ED[7:0]

0000

ADD+1 ADD+3

FRAME#

C/BE#

CS#

DEVSEL#

CLK

IRDY#

Figure 3-8. Legacy Bus DWORD Delayed Write Split Access for Byte Device