jeff@abnji.UUCP (jeff) (07/09/85)
[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 ! jeffcem@intelca.UUCP (Chuck McManis) (07/11/85)
> > 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. :-}
pollack@uicsl.UUCP (07/15/85)
Does anybody know how to get an RS232 interface off a board with only a +5 power supply? I thought -12 was needed... Jordan
irwin@uiucdcs.Uiuc.ARPA (07/16/85)
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.
tj@utcs.UUCP (tj) (07/17/85)
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
bill@persci.UUCP (07/19/85)
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
dale@wucs.UUCP (Dale Frye) (07/20/85)
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
mknox@UT-NGP.ARPA (mknox) (07/22/85)
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.
jb@terak.UUCP (John Blalock) (07/23/85)
> 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 \\\\\ -----> Soon to be part of CalComp, A Sanders Company