[comp.sys.acorn] BBC Microcomputer

cccph@jessica.cs.ucla.edu (Charles Hobbs) (05/16/91)

Is this the newsgroup a good place to find out about the Acorn
BBC microcomputer (6502 based 8-bit machine)? I picked up one of
these beasts at a flea market, and it seems to run ok, just would
like to know if there are any others still using this micro.

____________________________________________________________________
|Charles P. Hobbs           | BBC micro, Aquarius and Spectravideo
|cccph@jessica.cad.ucla.edu | users! Please email me! Thanks!
|Ham radio: N6YMK           | L.A. Blue Line Freq: 471.3375 mHz

gpvos@cs.vu.nl (Gerben 'P' Vos) (05/16/91)

cccph@jessica.cs.ucla.edu (Charles Hobbs) writes:

>Is this the newsgroup a good place to find out about the Acorn
>BBC microcomputer (6502 based 8-bit machine)?

Yes, certainly.

>                                              I picked up one of
>these beasts at a flea market, and it seems to run ok, just would
>like to know if there are any others still using this micro.

Tell us everything, ask us everything... We need more BBC stuff in this group.
The bad thing is that all BBC users a) already know everything they want to
know about the machine, or b) have bought an Archimedes instead; and probably
both.

. . . . . . . . . . . . . . . . . . . . . . . . . . . G e r b e n   V o s   <><
Aconet: BIGBEN!Gerben Vos  Internet: gpvos@cs.vu.nl
Acorn Electron rules!

cccph@jessica.cs.ucla.edu (Charles Hobbs) (05/17/91)

I apprieciate all of the information that the net has given be
about this computer....

I picked this machine up for about US $15 at a local flea market, with
no other documentation. (I've since been able to locate a few BBC
BASIC books in some libraries....) The machine has been modified
for 120 VAC, but not for NTSC (some screen lines go off the top of
the screen, and I can't get any color, just shades of gray).

I've looked at a few BBC basic textbooks, and the BASIC language
seems to be rich and powerful, somewhat more so than most of the
BASICs available on American machines.

Currently, the BBC operates alongside of an Atari 800, a TRS-80
color computer and a TI 99/4A. (I also have a Spectravideo and an
Aquarius, but haven't figured out what to do with those yet!)

I use these simpler 8-bit machines mostly for game playing and
some recreational programming, and I am interested in trading
public domain or user-written programs for all of these machines. 

More on the BBC micro:
1. How does one connect a cassette drive to it?
2. Is there a disk drive capability?
3. How about a modem port?

Thanks for your help.
P.S. I know there has been some trouble with bouncing mail from
some areas. Although my .sig says "send me e-mail", posting to this
newsgroup will be alright.

____________________________________________________________________
|Charles P. Hobbs           | BBC micro, Aquarius and Spectravideo
|cccph@jessica.cad.ucla.edu | users! Please email me! Thanks!
|Ham radio: N6YMK           | L.A. Blue Line Freq: 471.3375 mHz

Julian.Wright@comp.vuw.ac.nz (John Julian Wright) (05/17/91)

In article <2784@lee.SEAS.UCLA.EDU> cccph@jessica.cs.ucla.edu (Charles Hobbs) writes:

>1. How does one connect a cassette drive to it?

Look at the back of the machine. You will see three round sockets. The right
hand one in labled "Cassette", and you can plug a standard 5 pin din plug
into it (the other end of which is connected to your tape recorder). The two
outermost pins are the "motor control" pins and the "cassette" LED on the
front of the machine is illuminated when these two pins are shorted by the
internal relay. Motor control is not mandatory though.

Make sure you are in the tape filing system (enter "*Tape" at the '>' prompt)
and you can the use the LOAD and SAVE commands:
>LOAD"MyProgram"
  (at which point you start up the tape recorder and wait)
  or
>SAVE"MyProgram"
  (at which point you wind the tape to a blank spot, start it recording,
   and hit RETURN)

>2. Is there a disk drive capability?

If your machine has a disc drive interface then the start up message will
include the line "Acorn DFS" or similar. If not you will need to get a disc
interface kit from somewhere. The disc drive plugs into the 34 pin IDC plug
that can be found underneath the BBC, alongside the printer port, user port,
1MHz bus and Tube. Also you can power the disc drive from the power socket
underneath the power supply. (I don't have my manuals here so I can't give
you the pinouts sorry :-().

Once the disc drive and interface is installed, make sure you are in the disc
filing system (enter "*Disc" at the '>' prompt) and you can use the load and
save commands as above, except disc filenames can be only 7 characters in
length rather than 10 for tape, and you don't need to hit RETURN after the
SAVE command.

>3. How about a modem port?

There is an RS423 (RS232 compatable) port on the round socket next to the
cassette port.

Hope this helps somewhat! Give me a yell if you want the pinouts and I'll dig
around later for my user guide... :-)

    Cheers, Julian.
-- 
;`````````````````````````````````````````````````````````````````````````````;
; I would if I could but I can't so I won't but I might if I find I can later ;
;,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,;
jwright@comp.vuw.ac.nz                                julian@sideways.gen.ac.nz

gtoal@castle.ed.ac.uk (G Toal) (05/18/91)

In article <2771@lee.SEAS.UCLA.EDU> cccph@jessica.cs.ucla.edu (Charles Hobbs) writes:
.
.Is this the newsgroup a good place to find out about the Acorn
.BBC microcomputer (6502 based 8-bit machine)? I picked up one of
.these beasts at a flea market, and it seems to run ok, just would
.like to know if there are any others still using this micro.
.
.____________________________________________________________________
.|Charles P. Hobbs           | BBC micro, Aquarius and Spectravideo
.|cccph@jessica.cad.ucla.edu | users! Please email me! Thanks!
.|Ham radio: N6YMK           | L.A. Blue Line Freq: 471.3375 mHz


Quite a few of us actually, though the majority of discussion here is
about the Archimedes.  I'll try to find some interesting Beeb utils
to post soon; I'm afraid I've been quite busy lately.

Graham

hughesmp@vax1.tcd.ie (05/20/91)

In article <2784@lee.SEAS.UCLA.EDU>, cccph@jessica.cs.ucla.edu (Charles Hobbs) writes:
> 
>                                    The machine has been modified
> for 120 VAC, but not for NTSC (some screen lines go off the top of
> the screen, and I can't get any color, just shades of gray).

The grey (if I remember correctly) is adjustable using a link...
(Providing you are using the composite-video socket on the machine?)
I don't know which link it is - I've never owned one of the machines,
sadly... I think it may be near the video out... Then again, it may
only be in my imagination. Someone with a machine might be able to
comment? If it is there, moving it gives a colour output as opposed
to the standard monochrome...

Merlin.
--SICK--
You suffer... But why?

edb134t@monu6.cc.monash.edu.au (Daniel Bowen) (05/20/91)

In article <1991May20.034649.1@vax1.tcd.ie> hughesmp@vax1.tcd.ie writes:
>In article <2784@lee.SEAS.UCLA.EDU>, cccph@jessica.cs.ucla.edu (Charles Hobbs) writes:
>>                                    The machine has been modified
>> for 120 VAC, but not for NTSC (some screen lines go off the top of
>> the screen, and I can't get any color, just shades of gray).
>
>The grey (if I remember correctly) is adjustable using a link...
>(Providing you are using the composite-video socket on the machine?)
>I don't know which link it is - I've never owned one of the machines,
>sadly... I think it may be near the video out... Then again, it may
>only be in my imagination. Someone with a machine might be able to
>comment? If it is there, moving it gives a colour output as opposed
>to the standard monochrome...

It's link S39. Make the link for colour through the composite video output.
I use it on the rare occasion that I wish to video-tape the output
of ye olde Beeb..  It gives a better picture than the UHF out, and no
white-noise on the sound..  And of course if you decide you want to
record in monochrome, you can.

However, I DON'T think that this is the problem. I believe it may be
the incompatibility with NTSC that's causing this. But what would I know?


Daniel Bowen
-- 
Raymond Luxury-Yacht a.k.a. DANIEL BOWEN    |-- DISCOGRAPHY: You may also enjoy
Monash University, Melbourne, Australia |---| listening to a floppy disk called
edb134tbp2@vx24.cc.monash.edu.au |------| DSHD. You won't hear much, but people
edb134t@monu6.cc.monash.edu.au --| will stare at you.  [Toxic Custard Workshop]

osmith@acorn.co.uk (Owen Smith) (05/21/91)

In article <1991May20.034649.1@vax1.tcd.ie> hughesmp@vax1.tcd.ie writes:

>In article <2784@lee.SEAS.UCLA.EDU>, cccph@jessica.cs.ucla.edu
(Charles Hobbs) writes:

>>                                    The machine has been modified
>> for 120 VAC, but not for NTSC (some screen lines go off the top of
>> the screen, and I can't get any color, just shades of gray).

>The grey (if I remember correctly) is adjustable using a link...
>(Providing you are using the composite-video socket on the machine?)

Important question - is your machine a standard BBC micro or is it the
US variant? If it is the US variant it will have a large metal can
surrounding the PCB.

If you have the US variant then it really ought to produce colour - unless
as Charles says you have it connected to the composite video output and
you haven't connected the colour up (bit hard to do with the tin-can
round the circuit board though).

However, it sounds to me (from the 120 VAC conversion and the missing lines
off the top of the screen) that you have a standard BBC in which case I
think you are stuffed for colour on TVs (PAL and NTSC encoding are distinclty
incompatible). I'm surprised you get a picture at all, given that the
Beeb is outputting 50 Hz refresh frames and the TV is expecting 60 Hz. To
get colour you will need an RGB colour monitor - an EGA monitor for an
IBM PC should do the trick.

Owen.
 
The views expressed are my own and are not necessarily those of Acorn.

jhma@ukc.ac.uk (J.H.M.Aldridge) (05/22/91)

In article <1991May20.034649.1@vax1.tcd.ie> hughesmp@vax1.tcd.ie writes:
.. In article <2784@lee.SEAS.UCLA.EDU>, cccph@jessica.cs.ucla.edu (Charles Hobbs) writes:
.. ..  
.. ..                                     The machine has been modified
.. ..  for 120 VAC, but not for NTSC (some screen lines go off the top of
.. ..  the screen, and I can't get any color, just shades of gray).
.. 
.. The grey (if I remember correctly) is adjustable using a link...
.. (Providing you are using the composite-video socket on the machine?)
.. I don't know which link it is - I've never owned one of the machines,
.. sadly... I think it may be near the video out... Then again, it may
.. only be in my imagination. Someone with a machine might be able to
.. comment? If it is there, moving it gives a colour output as opposed
.. to the standard monochrome...

Some early BBC Micros did not have the link -- you had to solder a capacitor 
somewhere (I can't remember where after 8 years!) in the video section of the
board.

Even if you have the link, it seems very unlikely that you will be able to
display colour on an NTSC monitor as the machine puts out PAL composite
video.  Of course the RGB output should work .....

I can dig out any connection details if required.

--James

ajdh@stl.stc.co.uk (Andrew J D Hurley) (05/22/91)

In the referenced article hughesmp@vax1.tcd.ie writes:
>In article <2784@lee.SEAS.UCLA.EDU>, cccph@jessica.cs.ucla.edu (Charles Hobbs) writes:
>> 
>>                                    The machine has been modified
>> for 120 VAC, but not for NTSC (some screen lines go off the top of
>> the screen, and I can't get any color, just shades of gray).
>
>The grey (if I remember correctly) is adjustable using a link...

This is true, however, the composite video output is tuned to PAL, not
NTSC. Unless the machine has also been modified for NTSC the colour
encoding will be for PAL.

If my understanding of PAL vs NTSC is correct the upshot of all this is
that a colour PAL signal will come out as a mono picture on an NTSC set or
perhaps worse - ie completely wrong colours due to completely different
techniques of colour coding.

PAL codes colour by luminance (mono picture) and chrominance (a combination
of -blue and -red signals) the combination of which allows the calculation
of red, green and blue. I beleive NTSC is rather different and for all I
know the carrier frequencies are also different.

Maybe someone makes a simple converter to produce NTSC coded PAL frequency
signals from PAL ??

You are almost certainly better off trying to get an RGB to NTSC converter
which will plug into the BBCs RGB port so avoiding problems with
PAL colour coding.


-- 
Andrew J D Hurley,     ( ajdh@stl.stc.co.uk )
Mail route:   uunet!ukc!stl!ajdh  |  Phone:   +44 279 429531 x. 2535
BNR Europe Ltd., London Road, Harlow, Essex CM17 9NA, UK.

mre@ukc.ac.uk (M.R.Ellis) (05/24/91)

In artcile <4458@stl.stc.co.uk>,  ajdh@stl.stc.co.uk (Andrew Hurley) writes:
>In the referenced article hughesmp@vax1.tcd.ie writes:
>>In article <2784@lee.SEAS.UCLA.EDU>, cccph@jessica.cs.ucla.edu
>> (Charles Hobbs) writes:
>>> 
>>>                                    The machine has been modified
>>> for 120 VAC, but not for NTSC (some screen lines go off the top of
>>> the screen, and I can't get any color, just shades of gray).

The reason some lines appear to 'go off the top of the screen' is that your
television/monitor is expecting 272.5 lines between field sync pulses.  The
unmodified BBC micro gives 312.5 lines between field syncs - this is
because the UK television standard is 625 lines instead of the US standard
of 525 lines.  Fortunately your monitor can lock to the slightly different
signal it is being fed.  I am not aware of any way to correct this 'error'
in the BBC micro output.

>>The grey (if I remember correctly) is adjustable using a link...

The link is L39 on a BBC micro and L26 on the BBC B+.  If the required
link is not fitted to your machine,  a capacitor (470pF) should be
connected between the emitter of a BC239 and base of a BC309 in the
video circuit...on the B+ these transistors are Q9 and Q8 respectively,
I can't read the identifiers on my other schematics!!!

>This is true, however, the composite video output is tuned to PAL, not
>NTSC. Unless the machine has also been modified for NTSC the colour
>encoding will be for PAL.
>
>If my understanding of PAL vs NTSC is correct the upshot of all this is
>that a colour PAL signal will come out as a mono picture on an NTSC set or
>perhaps worse - ie completely wrong colours due to completely different
>techniques of colour coding.

This is correct.

>PAL codes colour by luminance (mono picture) and chrominance (a combination
>of -blue and -red signals) the combination of which allows the calculation
>of red, green and blue. I beleive NTSC is rather different and for all I
>know the carrier frequencies are also different.

Both PAL and NTSC encode the signal using the luma and chroma signals.  The
chroma signal is phase modulated onto a subcarrier and mixed onto the luma
signal.  In the standard PAL system (system-I) the subcarrier frequency is
approximately 4.43 MHz while the NTSC carrier is 3.58 MHz.  The phase of
one of the two colour difference signals is reversed on alternate lines in
the PAL method of coding,  hence the name!

The subcarrier frequency of the BBC micro output can be changed by changing
the 17.73 MHz crystal X2 (issue 7 BBC Micro and BBC model B+) for a
14.32 MHz crystal.  The phase alternation of the output should be inhibited
by disconnecting pin 12 of IC48 (BBC issue 7) and connecting it to 0V or
breaking the existing link S28 and making the alternative link S28 on a
model B+  (S28 is a three pad link with two pads linked by a copper track on
the PCB...the header may or may not be connected depending on the age of the
computer).

>Maybe someone makes a simple converter to produce NTSC coded PAL frequency
>signals from PAL ??

I've never heard of one at a reasonable cost...if they do exist they probably
decode the incoming signal to YUV (Americans may refer to similar signals as
YIQ) and re-encode these.  The cheapest way is probably to strip the incoming
signal right down to the RGB level!!

>You are almost certainly better off trying to get an RGB to NTSC converter
>which will plug into the BBCs RGB port so avoiding problems with
>PAL colour coding.

MOST RGB to NTSC coders will accept the BBC micro output so long as they are
fed with the syncs from the BBC micro.

PLEASE NOTE THAT :-

a)  I have NOT tried the modifications I have suggested...they come from
    theory and circuit diagrams and a small ammount of video experience.

b)  The pin numbers and component identities are taken from the only
    schematics I have...namely a BBC B (believed to be issue 7) and a 
    BBC B+ (only one issue released,  I believe).

c)  If anyone (at Acorn??)  can confirm/deny the advice given above,  I
    shall be most grateful to them for correcting any errors!!


--
Michael Ellis - Darwin College,  The University of Kent,  Canterbury,  England.

edb134t@monu6.cc.monash.edu.au (Daniel Bowen) (05/25/91)

In article <1594@mike.ukc.ac.uk> mre@ukc.ac.uk (M.R.Ellis) writes:
>>In the referenced article hughesmp@vax1.tcd.ie writes:
>>>The grey (if I remember correctly) is adjustable using a link...
>
>The link is L39 on a BBC micro and L26 on the BBC B+.  If the required

It's quite definitely S39 on my Issue 7 BBC B (I'm sitting in front of
the thing now!)


Daniel Bowen
-- 
Raymond Luxury-Yacht a.k.a. DANIEL BOWEN | Counselling on banana addiction
Monash University, Melbourne, Australia  |  is obtainable from a free
edb134tbp2@vx24.cc.monash.edu.au +-------+   information service run by
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