SCSI Core Operation
2-11
2.3.4 SCSI - DMA Transfers
In the SYM53C040, DMA handshaking with the SCSI core is handled
automatically by the DMA function. In order to initiate a DMA transfer to
the SCSI core using the DMA function in the SYM53C040, the following
sequence must be performed:
1.
The
register and the
and
address registers (
) must be written.
2.
The
register (
) is written with a 1 in the bit
0 (TIP) position.
3.
The firmware sets bit 0 in register 0x87 of the microcontroller core to
place the core in idle mode.
4.
The DMA waits for the microcontroller to enter the idle mode before
taking over the internal bus for memory reads or writes.
5.
Once the DMA receives a request from the SCSI core, the transfer
begins.
illustrates a target mode DMA transfer.
2.3.4.1 Halting a DMA Operation
Any SCSI or DMA interrupt, if enabled in the
register, terminates the DMA cycle for the current bus phase. It is
recommended that the DMA Mode bit be reset after receiving an
interrupt. The DMA Mode bit must be set before writing any of the Start
DMA registers for subsequent bus phases.
Summary of Contents for Symbios SYM53C040
Page 12: ...xii Preface...
Page 90: ...4 18 SCSI and DMA Registers...
Page 98: ...5 8 SFF 8067 Registers...
Page 110: ...6 12 Two Wire Serial Registers...
Page 126: ...7 16 Miscellaneous Registers...
Page 160: ...8 34 System Registers...
Page 184: ...9 24 Electrical Characteristics...
Page 194: ...A 10 Register Summary...
Page 214: ......
