neese@adaptex.UUCP (07/27/90)
>>Here is a summary of the information I received regarding AT bus scsi cards. >>Many thanks to the people that replied. > ... >>I have not included prices > > Best price I've seen on the 1542B is at Treasure Chest > (see ad in Computer Shopper for phone #) ... about $230 > >>Adaptec AHA1540B/1542B >>---------------------- >>* Maximum SCSI->AT transfer rate: 10M bytes/s (motherboard-dependent). >> (Bus master DMA, => card drives bus directly, not via the PC's DMA >> controller.) > > Where did this info come from ???? > I didn't see any info in the User Manual for the 1542B > to directly confirm this ... In the first sections a breif blurb about it is in there. > The board can be jumpered to set the DMA Transfer Speed > to 5.0, 5.7, 6.7, or 8.0 MB/s (via PINS 12,13 of the J5 Jumper Block) > (p. 2-9 of AHA-1540B/1542B User's Manual, Rev 1.0, April 1990). The jumper for 10MB/sec was not included as most systems cannot run this fast and the ones that can are not really running that fast as IOCHRDY will hold off the transfers and slow them down to what the CPU can really do. To be able to *really* do 10MB/sec DMA transfers then memory cycle time would have to be 100ns. That is not the speed of the ram, but the complete memory cycle time. Which means that the address setup time to read/write (leading edge) data would have to be about 23ns and IOCHRDY would have to be false during the entire cycle. > Not to mention, I don't understand this info, since the 1542B > seems to run OK on an ancient (circa 1988) MICRONICS 20 Mhz > motherboard which only supports 4 Mhz DMA transfer rate. The 4Mhz quote is for the motherboard DMA. This is the reason the 154x has its own DMA. Roy Neese Adaptec Senior SCSI Applications Engineer UUCP @ uunet!swbatl!texbell! {nominil,merch,cpe,mlite}!adaptex!neese