comp.sys.sinclair FAQ

In addition to the information provided here, several technical and service manuals are available that may be of interest to you. These cover the operation and configuration of these components in considerably more detail than is possible here. Please refer to the documentation page for links to these resources.

ULA:

• /CAS  1    40 GND        One of the +5V is decoupled through a RC-low-pass.
  /WR   2    39 Q          U,V are the color-difference signals.
  /RD   3    38 /MREQ      /Y is the inverted video including sync.
  /WE   4    37 A15        D are the data-lines, decoupled from the CPU by resistors.
  A0    5    36 A14
  A1    6    35 /RAS       T are the data-lines to the keyboard (address-lines through diodes)
  A2    7    34 /ROM CS
  A3    8    33 /IO-ULA    SOUND is the analog-I/O-line for beep, save and load.
  A4    9    32 CLOCK      CLK is the clock-source to the CPU including the inhibited T-states.
  A5   10    31 D7
  A6   11    30 D6         IO-ULA is (A0(CPU) OR /IORQ) for the I/O-port 0xfe
  /INT 12    29 D5         Q is the 14MHz-crystal, other side grounded through a capacitor.
  +5V  13    28 SOUND
  +5V  14    27 D4
  U    15    26 T4
  V    16    25 D3
  /Y   17    24 T3
  D0   18    23 T2
  T0   19    22 D2
  T1   20    21 D1

AY-3-8912 Sound Chip:

• SOUND C   1    28  D0       Vcc is +5V.
  PORT      2    27  D1       SOUND A, B and C can be tied together.
  Vcc       3    26  D2       CLOCK can be some MHz.
  SOUND B   4    25  D3
  SOUND A   5    24  D4
  GND       6    23  D5
  PORT      7    22  D6
  PORT      8    21  D7
  PORT      9    20  BC1
  PORT     10    19  BC2
  PORT     11    18  BDIR
  PORT     12    17  A8
  PORT     13    16  RESET
  CLOCK    14    15  CLOCK

Keyboard Layout:

•   OUTER SIDE   A 15 14 8  13 12 9  10 11  INNER SIDE
               D
               0   BR EN CS P  0  A  Q  1
               1   SS L  Z  O  9  S  W  2
               2   M  K  X  I  8  D  E  3
               3   N  J  C  U  7  F  R  4
               4   B  H  V  Y  6  G  T  5
    INNER SIDE
  
    [BR] BREAK   [EN] ENTER   [CS] CAPS SHIFT   [SS] SYMBOL SHIFT

128K Composite Video Output:
Pin 1 is composite PAL, 2 is GND. There's no audio on any pin of the RGB connector.

The picture is a bit dull unless your TV's video input is High Z (high impedance) However, that's quite unlikely. Normally the impedance of the video input is around 75 Ohms. To alleviate this problem, short the 68 Ohms resistor inside the Speccy that's in series with pin 1 (follow the track on the PCB). Or you can hook it directly to the input of the RF modulator.

The audio can be taken from the MIC socket but a better balance between 48K and 128K sound is obtained directly from pin 5 of IC38.

128K RGB Video:

• 128K ZX Spectrum:

          RGB              Pin  Signal              Level
                           -------------------------------------------------
     --7--   --6--         1    Composite PAL       75 Ohms, 1.2 Volts pk-pk
           |               2    0 Volts DC
      3--  8  --1          3    Bright output       TTL
    --     |     --        4    Composite sync      TTL
        /     \            5    Vertical sync       TTL
       5   |   4           6    Green               TTL
      /    2    \          7    Red                 TTL
           |               8    Blue                TTL

• ZX Spectrum +2A / +3:

          RGB              Pin  Signal              Level
                           -------------------------------------------------
     --7--   --6--         1                        +12V
           |               2    GND                 0V
      3--  8  --1          3    Audio Out
    --     |     --        4    /Composite Sync     TTL
        /     \            5                        +12V 
       5   |   4           6    Green               Analogue 1.67V p-p
      /    2    \          7    Red                 Analogue 1.67V p-p
           |               8    Blue                Analogue 1.67V p-p

Power Supplies:
Information about hardware and peripherals with entries elsewhere in this FAQ can be found on the appropriate pages.

• Machine             Voltage   Amperage  Centre Polarity
  -------------------------------------------------------
  ZX81                 9V DC     500 mA        +ve
  Timex 1000/1500      9V DC     500 mA        +ve
  TC 2048              9V DC     800 mA        -ve
  TC 2068              9V DC     1.0  A        -ve
  TS 2068             15V DC     1.0  A        -ve
  Z88                6.5V DC     500 mA        +ve
  Flat-screen TV     5.9V DC     100 mA        -ve

ZX Interface I RS-232: The RS-232 socket provided on the ZX Interface I has the following configuration:

1. Not Connected.
2. TX Data - Input.
3. RX Data - Output.
4. DTR - Input. This should be high when ready.
5. CTS - Output. This should be high when ready.
6. Not Connected.
7. Ground. Pull down.
8. Not Connected.
9. +9v - Pull up.

/----------------------\
\ 5 o   o   o   o   o 1/
 \  9 o   o   o   o 6 /
  \------------------/

• (Pin 2) - TX Data.
• (Pin 3) - RX Data.
• (Pin 5) - CTS.
• (Pin 6) +9V - Normally DSR.
• (Pin 7) - Ground.
• (Pin 20) - DTR.