MSG

C_D

I_O

SCSI Phase

 

 

 

 

0

0

0

Data-Out

0

0

1

Data-In

0

1

0

Command

0

1

1

Status

1

0

0

Reserved-Out

1

0

1

Reserved-In

1

1

0

Message-Out

1

1

1

Message-In

 

 

 

 

TC[23:0] Transfer Counter[23:0]

This 24-bit field specifies the number of data bytes to be moved between the LSI53C810A and system memory. The field is stored in the DMA Byte Counter (DBC) register. When the LSI53C810A transfers data to/from memory, the DMA Byte Counter (DBC) register is decremented by the number of bytes transferred. In addition, the DMA Next Address (DNAD) register is incremented by the number of bytes transferred. This process is repeated until the DMA Byte Counter (DBC) register has been decremented to zero. At that time, the LSI53C810A fetches the next instruction.

If bit 28 is set, indicating table indirect addressing, this field is not used. The byte count is instead fetched from a table pointed to by the Data Structure Address (DSA) register.

6.3.2 Second Dword

Start Address

[31:0]

This 32-bit field specifies the starting address of the data to be moved to/from memory. This field is copied to the DMA Next Address (DNAD) register. When the LSI53C810A transfers data to or from memory, the DMA Next Address (DNAD) register is incremented by the number of bytes transferred.

When bit 29 is set, indicating indirect addressing, this address is a pointer to an address in memory that points to the data location. When bit 28 is set, indicating table

6-12

Instruction Set of the I/O Processor

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LSI 53C810A technical manual Second Dword, TC230 Transfer Counter230, Start Address 310