Article-I.D.: abnji.732
Posted: Tue Jul  9 09:48:19 1985
Date-Received: Thu, 11-Jul-85 07:29:15 EDT
Lines: 33

[batteries to power, turbines to speed...]

	I am considering the purchase of the Servo 8 single board Z80
system.  It features:
	. Z80 B with 64K 150nS DRAM
	. +5 volts only at 1.4 amps
	. 2 RS232 ports
	. 1 Centronics port
	. SASI bus
	. can operate 4:5.25" and 4:8" drives at the same time
	. built in Debugger in EPROM

	The only competing product I see is the new Little Board
(t.m. of Ampro Computers).

1)  Does anybody have any first hand information on either of the
	above or similar boards?
2)  The Servo is approx. $600 for everything.
	The Little Board is $350 + $100 for the SCSI adapter,
	but it is a Z80 A (4 Mhz).

	I am deciding which to buy.  I favor the Servo system
since it is all integrated, faster and +5 volt only,
but that is not taking into account the company's and
product's reliability.

	Have any of you made a similar choice?

	What is the difference between the SASI and SCSI busses?

			Jeff 'very soft and furry' Skot
			at the microprocessor based ATT IS Somerset
			{ihnp4 | mcnc | cbosgb} abnji ! jeff

Article-I.D.: intelca.17
Posted: Thu Jul 11 13:40:57 1985
Date-Received: Sat, 13-Jul-85 11:32:20 EDT
References: <732@abnji.UUCP>
Organization: Intel, Santa Clara, Ca.
Lines: 67

> 
> 	I am considering the purchase of the Servo 8 single board Z80
> system.  It features:
      ... List some features ...
> 
> 	The only competing product I see is the new Little Board
> 
> 1)  Does anybody have any first hand information on either of the
> 	above or similar boards?

  I own a "Little Board" so yes the information is "First Hand" (left to
  be specific :-))

> 2)  The Servo is approx. $600 for everything.
> 	The Little Board is $350 + $100 for the SCSI adapter,
> 	but it is a Z80 A (4 Mhz).
 
  Looks like the L.B. is $150 cheaper, just so happens that is the exact
  cost of the Integrand enclosure designed for it.

> 	I am deciding which to buy.  I favor the Servo system
> since it is all integrated, faster and +5 volt only,
> but that is not taking into account the company's and
> product's reliability.

  Of your three points a.) More integrated may also mean larger, the 
  L.B. has the identical form factor to a 5-1/4" disk drive so that
  it can be mounted on top of one, additionally I believe the L.B. plus
  has the SCSI adapter builtin to the system. c.) 5 Volt only is great
  if you are not running this thing with a disk, since the standard 
  minifloppy power supply provides +5 and +12 you can run the L.B. from
  the same supply that is running the disk. Note : the little board 
  cannot control 8" drives. As for reliabilty I believe they are both
  relatively new, Ampro less so. There is a thriving user community and
  Ampro does provide a generous amount of software such as CP/M 2.2 and
  ZCPR3 (which is pretty damn powerful) I don't know if Servo provides
  any such.

> 	Have any of you made a similar choice?
 
  Yes.

> 	What is the difference between the SASI and SCSI busses?

  The Small Computer System Interface (SCSI) is an outgrowth (ie ansi
  standard) of the Shugart Associates Systems Interface. It is mostly
  upward compatible. The Ampro people extend it a little further than 
  that for their own purposes while still maintaining compatiblity.

> 			Jeff 'very soft and furry' Skot
> 			at the microprocessor based ATT IS Somerset

More and more of these systems are appearing (makes you wonder about
CP/M sometimes) and the level of integration is getting amazing. For
a bit more CPU power Ampro announced the Little Board/186 which is
based on the 80186, has .5 Mbytes of RAM and the SCSI builtin. It 
is also the same form factor as the 5-1/4" disk drive. Don't know
what they will be selling them for.

[Not affiliated with Ampro just happen to have some info.]

--Chuck
-- 
"Unix, the Teco of Operating Systems."      - - - D I S C L A I M E R - - - 
{ihnp4,fortune}!dual\                     All opinions expressed herein are my
        {qantel,idi}-> !intelca!cem       own and not those of my employer, my
 {ucbvax,hao}!hplabs/                     friends, or my avocado plant. :-}

Article-I.D.: uicsl.7000006
Posted: Mon Jul 15 12:18:00 1985
Date-Received: Wed, 17-Jul-85 08:02:54 EDT
References: <732@abnji.UUCP>
Lines: 10
Nf-ID: #R:abnji.UUCP:-73200:uicsl:7000006:000:130
Nf-From: uicsl.UUCP!pollack    Jul 15 11:18:00 1985






Does anybody know how to get an RS232 interface off a board with
only a +5 power supply? I thought -12 was needed...


Jordan

Article-I.D.: utcs.754
Posted: Wed Jul 17 09:30:13 1985
Date-Received: Wed, 17-Jul-85 10:23:32 EDT
References: <732@abnji.UUCP> <7000006@uicsl>
Reply-To: tj@utcs.UUCP (tj)
Organization: University of Toronto - General Purpose UNIX
Lines: 11
Summary: 


May a thousand engineers congregate at my door if I am wrong.

To the best of my knowledge what you probably have is an EIA interface.
EIA is the same as 232 except it is TTL levels (gross simplification).
It is possible to get true rs232 from 5 volt supply by adding a small
supply inverter module on the board. It takes +5 volts and gives you
-12 volts using a small transformer and a switching type arrangement.
A lot of equipment doesn't really give a true -12 for rs232, but a lot
of equipment also doesn't require -12 on input!
t.jones

Article-I.D.: uiucdcs.10400197
Posted: Tue Jul 16 10:37:00 1985
Date-Received: Thu, 18-Jul-85 05:34:54 EDT
References: <732@abnji.UUCP>
Lines: 8
Nf-ID: #R:abnji.UUCP:-73200:uiucdcs:10400197:000:435
Nf-From: uiucdcs.Uiuc.ARPA!irwin    Jul 16 09:37:00 1985


It is easy to generate an on board voltage for RS-232. The current drain
is not much, so a 555 timer can be used as an oscillator, a couple of
diodes and capacitors to form a voltage doubler and presto, one 12 volt
supply. This can be done to form a plus or minus supply. Back when the
DRAMS had two voltages, I purchased a 128k memory board that had the
second voltage for the memory chips generated in this fashion. It worked
great.

Article-I.D.: persci.246
Posted: Fri Jul 19 10:37:14 1985
Date-Received: Sun, 21-Jul-85 04:19:57 EDT
References: <732@abnji.UUCP> <7000006@uicsl>
Reply-To: bill@persci.UUCP (Bill Swan)
Organization: Personal Scientific, Woodinville WA
Lines: 14
Summary: 

In article <7000006@uicsl> pollack@uicsl.UUCP writes:
>Does anybody know how to get an RS232 interface off a board with
>only a +5 power supply? I thought -12 was needed...
>Jordan

To build a proper interface, you do. The RS-232 spec says that you should
drive the lines between +/- 5V (minimum). In practice, most RS-232 receivers
have a threshold of about 1 volt, which means that in a pinch you could drive
the line with TTL directly. Not a great practice, but it (usually) works.

Otherwise, you need to provide -12V, which can be done with a DC-DC converter.

-- 
Bill Swan 	{ihnp4,decvax,allegra,...}!uw-beaver!tikal!persci!bill

Article-I.D.: wucs.1041
Posted: Fri Jul 19 18:59:20 1985
Date-Received: Sun, 21-Jul-85 21:20:42 EDT
References: <732@abnji.UUCP> <7000006@uicsl>
Organization: Washington U. in St. Louis, CS Dept.
Lines: 15

In article <7000006@uicsl>, pollack@uicsl.UUCP writes:
> 
> 
> 
> 
> 
> Does anybody know how to get an RS232 interface off a board with
> only a +5 power supply? I thought -12 was needed...
> 
> 
> Jordan

Use a DC - DC converter. Check the usual electronic supply houses.

Dale Frye @ Washington University in St. Louis

Article-I.D.: brl-tgr.61
Posted: Sun Jul 21 21:46:21 1985
Date-Received: Tue, 23-Jul-85 04:52:37 EDT
Sender: news@brl-tgr.ARPA
Lines: 5


Actually, although most RS232 interfaces do use +12, +5, and -12 VDC
inputs, it is quite simple to do DC-to-DC conversion with a couple of
transistors (or a big buffer IC).  This allows you to generate the
relatively low current -12 and +12 VDC from the +5.

Article-I.D.: terak.645
Posted: Tue Jul 23 11:58:11 1985
Date-Received: Thu, 25-Jul-85 23:20:21 EDT
References: <732@abnji.UUCP> <7000006@uicsl>
Organization: Terak Corporation, Scottsdale, AZ, USA
Lines: 24

> Does anybody know how to get an RS232 interface off a board with
> only a +5 power supply? I thought -12 was needed...

Both +12v and -12v are needed if you want true RS232 levels.  The RS232 spec
defines a space (logic 0) as +3 to +15v and a mark (logic 1) as -3 to -15v.
However, most RS232 equipment doesn't need these levels to work properly.
If the equipment you are driving uses a 1489 line receiver (and most do these
days) you can get away with standard TTL levels.  The 1489 logic low threshold
is specified to be between +0.75 and +1.25 volts.  For short runs you can drive
the "RS232" line with a 7404 (remember you need to invert the logic levels).
For somewhat longer lines, I recommend using a 7405 or 7406 open collector
inverter with a on-board pull up resistor of ~2K.  Neither will give you the
capability to drive lines as long as standard RS232 drivers can drive, nor will
you have the noise immunity of standard RS232.  But to drive a < 10-foot line to
a local terminal or printer I've never experienced any problems using TTL
voltage levels except with equipment that didn't use the 1489 line receivers..

John Blalock, W7AAY

uucp:	 ...{amd,decvax,hao,ihnp4,seismo}!noao!terak!jb
phone:	 (602) 998-4800
us mail: Terak Corp., 14151 N. 76th St., Scottsdale, AZ 85260
         \\\\\
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