Command Descriptor Block
Byte 03 Least Significant byte of the Logical Byte 04 xxxxxxxx Operation Length Usually Sector count in Data Request Used by the Peripheral Target to request a DMA data transfer. Direction of transfer is determined by the R _W signal. A 3-bit number designating the physical controller receiving the Command Block. Up to eight 0 through 7 controllers can be connected to the Atari DMA channel. Usually set on target device with dip switches or jumpers. A 5-bit number specifying the operation...
Walt for Acknowledge
Once the byte has been sent, wait for an acknowledge from the target device by monitoring bit 5 of the GPIP General Purpose Interrupt Port of the MC68901 . Bit 5 is cleared when the target device is ready for the next byte. This operation should also timeout in case a response is not obtained from the target device. See the programming example above for an example of how to do this. The following programming example combines a required 20 microsecond delay between command bytes with the 3...
ACSI Bus Signals and Descriptions
These 8 active high signals are the data bits. Used by the peripheral to request a DMA data transfer. This line is used to request a byte of data during the DMA data transfer. The direction of the transfer is identified by the R _W signal which is controlled by the DMA Read Write bit in the DMA Mode Control Register. _DRQ is driven by the peripheral with an open collector output. Only the peripherals that have been commanded by the host peripheral may drive JRQ, _DRQ, or the data bus. A...
ACSI and SCSI The Differences
Some important differences between ACSI and SCSI Physical cable connection - ACSI uses a 19 pin shielded cable versus the 50 pin flat ribbon cable used by SCSI. The master slave relationship - This defines who is in charge of bus operations between the computer and its peripherals. The ACSI bus specifies that the host computer is always in control of the bus as opposed to SCSI which allows both computers and peripherals to initiate control of the bus . Maximum cable length - ACSI allows a...