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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. Several sections currently listed here will be incorporated into other entries in this FAQ during later revisions.
In addition, an updated ZX Interface I entry will be available shortly.
ULA:
-
/WR 2 39 Q One of the +5V is decoupled through a RC-low-pass.
/RD 3 38 /MREQ U,V are the color-difference signals.
/WE 4 37 A15 /Y is the inverted video including sync.
A0 5 36 A14 D are the data-lines, decoupled from the CPU by resistors.
A1 6 35 /RAS
A2 7 34 /ROM CS T are the data-lines to the keyboard (address-lines through diodes)
A3 8 33 /IO-ULA
A4 9 32 CLOCK SOUND is the analog-I/O-line for beep, save and load.
A5 10 31 D7 CLK is the clock-source to the CPU including the inhibited T-states.
A6 11 30 D6
/INT 12 29 D5 IO-ULA is (A0(CPU) OR /IORQ) for the I/O-port FEh
+5V 13 28 SOUND Q is the 14MHz-crystal, other side grounded through a capacitor.
+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
| .gif images of the pin configuration and layout of the ULA are available from the World of Spectrum | AY-3-8912 Sound Chip:
| note that the AY-3-8912 used in the Timex TS2068 runs at 1.76475Mhz | Keyboard Layout:
| in reality, the matrix connections are in one row on the top side of the membrane |
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 in this section will be incorporated into the corresponding hardware
and peripherals pages during subsequent revisions.
The pin configuration of the +2a/+3 PSU lead is:
---u---
/ \
/ +5 -12 \
| 0 |
\ +5 +12 /
\ +12 /
-------
The 5V line is rated at 2A, the +12V at 700mA (200mA for the +2a) and the -12V at 50mA.
ZX Interface I RS-232: - Pending
Information in this section will be incorporated into the main ZX Interface I
entry during subsequent revisions. Additional information is also available that enhances this entry. This will be incorporated shortly.
The RS-232 socket provided on the ZX Interface I has the following configuration:
- Not Connected.
- TX Data - Input.
- RX Data - Output.
- DTR - Input. This should be high when ready.
- CTS - Output. This should be high when ready.
- Not Connected.
- Ground. Pull down.
- Not Connected.
- +9v - Pull up.
/----------------------\
\ 5 o o o o o 1/
\ 9 o o o o 6 /
\------------------/
An RS-232 cable will be required to connect to other peripherals. This must be wired as follows:
- (Pin 2) - TX Data.
- (Pin 3) - RX Data.
- (Pin 5) - CTS.
- (Pin 6) +9V - Normally DSR.
- (Pin 7) - Ground.
- (Pin 20) - DTR.
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