What computer system is this from 1984 Doctor Who?

Question

In the 1980s, the popular BBC science fiction series Doctor Who used some real computer system(s) to display impressive (for the time, OK, maybe not!) graphics. They actually ran the software real-time and simply filmed the output on the screen.

Most of the time they filmed the screen while the program was already running, but on a couple of occasions they showed the source code briefly before the program was run, presumably because it made the story look more science-fictiony!

Source code

TA&7A
  360.AP:LDX&78:LDY#0:.AD:LDAM%,X:STA(&7
6),Y:CLC:TYA:ADC#8:TAY:DEX:BNEAD
  370CLC:LDA&76:ADC#1:STA&76:LDA&77;ADC#
0:STA&77
  380DEC&7B:BNEAQ:CLC:LDA&74:ADC&82::STA
&74:STA&76:LDA&75:ADC&83:STA&75:STA&77:L
DA#8:STA&7B:.AQ:DEC&7A:BNEAP
  390CLC:LDA&72:ADC#1:STA&72:LDA&73:ADC#
0:STA&73
  400DEC&7F:BEQAZ:JMPAA:.AZ:RTS:]:NEXT:E
NDPROC
  410DEF PROCtitle
  420REPEATUNTILINKEY(0)=32
  455Xsize=4:Ysize=4:YOUR$="_______":PRI
NTTAB(6,7);:PROCdisplay
  460Xsize=4:Ysize=4:YOUR$="X.V.773":PRI
NTTAB(6,6);:PROCdisplay
  461REPEATUNTILINKEY(0)=32
  465Xsize=2:Yzise=2:YOUR$="LAST LOCATIO
N: 27|43":PRINTTAB(0,14);"PROCdisplay
  466REPEATUNTILINKEY(0)=32
  467Xsize=2:Ysize=2:YOUR$="LAST CONTACT
 : 12-99":PRINTTAB(0,20);:PROCdisplay
  470REPEATUNTILINKEY(0)=32
  475Xsize=2:Ysize=2:YOUR$="____________
______":PRINTTAB(2,29);:PROCdisplay
  480Xsize=2:Ysize=2:YOUR$="BELIEVED DES
TROYED":PRINTTAB(2,28);:PROCdisplay
  520FORW=0TO 4E3:NEXT:
  610ENDPROC
>RUN

Output

Amusingly, the command prompt is visible at the end of the final underline!

Stories that feature running software on '80s computers (probably an incomplete list):

• 1982 - Castrovalva (filmed late 1981)
• 1983 - The Five Doctors
• 1984 - The Twin Dilemma (pictured above)
• 1985 - Attack of the Cybermen (filmed late 1984)

Although the computers used were not necessarily the same, I would be interested in knowing what system is pictured below. It's using some combination of BASIC and assembly language that I don't recognise.

Things I have been able to work out:

• The screen is 40 characters by 32 characters.
• Lines 350-400 (and probably earlier) contain assembly language
  • It appears that the assembly is embedded into the BASIC program and wrapped in [ and ] characters, but it's hard to tell from a single screenshot
• Lines 410-610 contain a full procedure, which is the "controller" of the code (in MVC terminology)
• The underline is printed before and one line below the actual text, presumably to prevent the text from being deleted by the blank space above the underline characters!
• Xsize and Ysize are how much to stretch the text in in each direction and YOUR$ (pronounced "your string") contains the text to display
  • PROCdisplay is a procedure that displays your string at the current location with x size and y size
• PRINTTAB (probably just PRINT TAB with an optional space removed and not a separate command) places the text cursor at the position specified on the screen
• The coordinate system starts at the bottom left, and works upwards and to the right
  • This means you can PRINT "Hello " normally, then immediately PROCdisplay "Fred" at twice the size without having to reposition the text cursor
• REPEATUNTILINKEY(0)=32 (REPEAT UNTIL INKEY(0) = 32) polls the keyboard until the [Space] is pressed, at which point the return value of INKEY(0) is ASCII 32 for space
  • The way INKEY(0) works is exactly the same as Locomotive BASIC on the Amstrad CPC series but the rest of the grammar is incompatible
• Integers, and possibly floating point numbers, may be typed in scientific notation. On line 520 4E3 is 4000 for a saving of one character!

What is this computer, and what BASIC and assembly language is it? All transcription errors are my own!

Answer 1

This is an example of BBC BASIC with inline (6502) assembler code. The computer in use would have been a BBC Microcomputer, manufactured by Acorn Computers Ltd.

The display was probably a studio monitor of some sort. These could be driven directly using either the RGB output or the composite video output of the microcomputer. It is likely that the actual BBC Micro was not shown in the programmes but, nevertheless, this is what would have been used for generating the display signal.

BBC technicians had a lot of influence on the specification of the BBC Micro, since they wanted to make use of the machines in their studios and labs. The machine wasn't just designed for schools and colleges.

It is likely that the BBC Micro would have had a Genlock board fitted to prevent strobing when the monitor was filmed by a television camera.

Both the BBC Micro and BBC Basic were designed by Sophie Wilson.

Answer 2

There is some information what the BBC did at that time with BBC Micros in the archive of the Computer Literacy Project.

Subtitling, there they show a glimpse of a BBC Micro with a board to sync it with the equipment in the studio: https://clp.bbcrewind.co.uk/20508b5e272e398cf9579181e594e8e2

You can have a look at their programs running and even their source code: https://clp.bbcrewind.co.uk/jsbeeb/index.html?disc1=CLP0038.ssd&loadBasic=%2Fbeeb%2Floader%2F20508b5e-272e-398c-f957-9181e594e8e2&autorun=1&model=Master

Or the end titles of Making Most of the Micros: https://clp.bbcrewind.co.uk/jsbeeb/index.html?disc1=CLP0038.ssd&loadBasic=%2Fbeeb%2Floader%2F3e5b356d-cf22-09bd-ba89-0ec4287f32dd&autorun=1&model=Master