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CD Burning SCSI and Parity

Posted on 1998-01-07
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Last Modified: 2010-04-12
I have a Ricoh MP6200S accompanied by a Segate 1GB SCSI drive along with a 2940 Standard PCI controller

what im wondering is how to set these up PERFECTLY without any problems (im making coasters :~(

CURRENTLY the card is terminated, as is the SCSI HDD butthe CD-R is not

Parity is ON on the HDD and also it is jumpered to
"drive receives power from SCSI Bus AND power cable"

where can i learn about parity on the SCSI bus and also power via the scsi bus options?

how should these be set?

and how should i setup the cards bios? it has many options including adjust the Sync transfer rate termination and so on as well

this is the SECOND CD-R of this model that has had this problem so im now at the point of thinking its the SCSI setup or the machine itself

here are some other details on the machine

ABIT IT5H
64MB 60 NS EDO RAM
6.4 GB IDE WD Primary Master (but system is set to boot off the 1gb SCSI)
4MB STB 968 based velocity card
OSR 2 + Easy CD Pro 2.11c being used (also using image files and also the burn passed the test)
AHA 2940 S76 - 1.23 bios revision
166MMX CPU

I also have a SECOND machine which i burn cd's on regularly, so i know what im doing etc etc

the machine is not running "too many tasks at the time"
no screen saver either

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Question by:abrasion
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Expert Comment

by:jhance
ID: 1122513
Parity, or the lack thereof, is not causing your problem as described above.  Either the parity is working or it's not.  If it's not, then you would be getting errors all of the time and you would know there was a problem.  Many SCSI devices ignore parity anyway.  It could be that your SCSI bus is not configured properly (i.e. terminations).  It should be like this:

TERM-CONTROLLER---------SCSI DRIVE-------SCSI DRIVE-TERM

The terminators must be at the far ends of the cable.  Usually, the one at the controller is at one end but not always.  If you have an internal/external setup it mus be like this:

TERM----EXT DRIVE----CONTROLLER-----INTERNAL DRIVE----TERM

You may need to remove or disable terminators from the controller.  Some controllers don't support internal/external operations even though it appears that they can.  I think yours is OK but read the docs carefully to be sure.  Some controllers don't have any terminators at all and you must put one on the external connector even if there are no external devices out there.  Again, read the docs.

Another area of problems is the cable itself.  Be sure that yours is good and of good quality.  There are a lot of junk cables out there.

Also, I couldn't find the specs on the Ricoh CD-R but does it have a substandard amount of internal RAM?  In my experience, if the internal RAM is < 1MB, you're luck if it works at all, much less on a system where the CD-R and the HDD are sharing the same SCSI bus.
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Author Comment

by:abrasion
ID: 1122514
I know how termination works, its why im begging to love SCSI fairly straight forward.

But the CDR, the HDD and the CARD .. what does PARITY mean? is it a byte checking enabled to guaruntee the data goes thru nicely? or what i need to UNDERSTAND it to truely know how to handle it in all situations

Termination is ok but why termination power whats that?

and when u jumper them with the power config why do u tell your HDD its recaiving power from a cable and the SCSI bus does the SCSI bus naturally have 5 / 12 volts thru it?

when i understand all this some1 will have 600 points .. please give me a fully detailed technical answer im here to learn :)
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Expert Comment

by:jhance
ID: 1122515
Parity - On the SCSI bus there are 8 data bits and 1 parity bit.  It is generated from the other 8 bits so that the number of "1"s in the full 9 bits is either odd or even.  Hence odd-parity or even-parity.  Again, this is likely not your problem.  If the parity were wrong nothing would work.  Most devices have a jumper which selects whether parity should be checked or not.  Most SCSI adapters had some type of parity checking circuitry on them.  It tells the host or device that there was some upset on the bus.  

Termination Power - SCSI was first conceived it used terminators.  That is resistors from the signal lines to +5V and Ground.  These condition the signals so that less noise is generated and things can run faster.  The power to the +5V side of the terminator has to come from somewhere.  Generally this is supplied from the host computer.  A problem arose when people (especially Apple) started attaching SCSI devices to battery powered computers.  The SCSI terminators draw a lot of power and drained the batteries quickly.  So laptop computer manufacturers stopped supplying power to the SCSI bus.  It was up to the SCSI peripheral manufacturers to get their own power.  Today, most devices can supply their own terminator power.  It's usually selectable from a jumper inside the device.  It is NOT a good idea to have terminator power from both the host and the SCSI device.  Since you have two +5V supplies driving each other, it usually generates noise on the SCSI but and this is a bad thing.

Let me know if you need further clarification.
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Author Comment

by:abrasion
ID: 1122516
You have just about got these points Jhance but ill make u work for them and i really want to learn here

so what your saying is .. parity .. always have on? .... is there any situation where parity off would be of use OR neccessary?

 and as for termpower ... with the 2940? ..... how do i set this turn the term power OFF on the devices and on on the terminated card? .. obviously on NON terminated devices (my cdr is unterminated id 6, hdd is terminated id0 and controller is terminated id7) such as my CDR no termpower at all ? but termpower on,  on the HDD?

so how would YOU setup my system

2940
Segate 1gb with jumpers for parity, termination and also jumpers for "power from scsi only" "power from cable only" and "power from both"
and a CW-7501 Panasonic drive with termination parity and termpower jumpers also
?

then the points are yours

please note im not doing this to aggrevate nor test u .. merely to learn .... so that i too can one day burn good cd's ..... and make money in the harwdware industry

thanks again


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Accepted Solution

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jhance earned 600 total points
ID: 1122517
I'll will be glad to continue until your're clear:

so what your saying is .. parity .. always have on? .... is there any situation where parity off would be of use OR neccessary?

I'm saying that it doesn't matter at all as long as ALL the devices on the SCSI bus are in agreement as to whether to use parity or not.  Since it's generated in the hardware of the SCSI interface, there is no performance penalty one way or the other.  Myself, I'd turn it off because most systems don't use it anyway and it's just something else to go wrong.  You controller, however, may not have the option of turning it off.  It may be easier to just leave the controller alone and set all of the devices to match it.

and as for termpower ... with the 2940? ..... how do i set this turn the term power OFF on the devices and on on the terminated card? .. obviously on NON terminated devices (my cdr is unterminated id 6, hdd is terminated id0 and controller is terminated id7) such as my CDR no termpower at all ? but termpower on, on the HDD?

Again, you can do it either way but it is vital that ALL things plugged into the SCSI bus are doing it the SAME way.  For a desktop system, I always setup the SCSI termination power from the controller.  This is mostly for convenience since most SCSI devices come with "supply term power" off by default and there are a few out there that cannot do their own "term power".  

2940
Segate 1gb with jumpers for parity, termination and also jumpers for "power from scsi only" "power from cable only" and "power from both"
and a CW-7501 Panasonic drive with termination parity and termpower jumpers also
?

To summarize, I'd configure your system like this (I assume that BOTH the Seagate and Panasonic are internal devices):

2940 - Parity on, terminator installed (if at the end of the SCSI chain) and supplying terminator power.

Seagate 1GB - Parity on, no terminator, no term power.

Panasonic - Parity on, terminator installed, no term power.

The bus should look like this physically:

TERM-2940---SEAGATE----PANASONIC-TERM
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Author Comment

by:abrasion
ID: 1122518
good man ....... looks like i have to make some changes eh ?

while im at it, do you know how to measure the actual TRUE wattage of a power supply?.... alot of "230's" are remarked 200's (on the curcuit board inside) and how do i know if im running too many devices off one (occasional crashes

thanks for your time :)

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