Sinclair QL
The Sinclair QL (for Quantum Leap) is a personal computer launched by Sinclair Research in 1984, as an upper-end counterpart to the ZX Spectrum. The QL was aimed at the serious home user and professional and executive users markets from small to medium-sized businesses and higher educational establishments. It was a very promising and inventive machine, based on the 68008 processor from Motorola. Although it succeeded in becoming the first home computer based on a 32-bit CPU, the rush to market resulted in it being plagued by many problems from the start. After commercial disappointment, UK production was suspended in 1985 and finally discontinued in April 1986.
Contents
Models
There are two main versions of the QL are in circulation.
- A certain number of boards to build standards up to Issue 5 were issued in either ROM or EPROM versions, sometimes referred to as pre-Issue 6.
- The second, volume production, version of the board to build standard Issue 6, and subsequent, sometimes referred to as post-Issue 6.
There are also geographic variants.
- European
- North American
Video Information
The QL provides various video output capabilities. Two video modes are available:
- 256×256 pixels (65,536 total) with 8 RGB colours and per-pixel flashing. Pixel aspect ratio was appx. 4.4:3 (i.e. 1.466) making the image extend into the horizontal overscan area of a TV. This has the designation 0.07M3.
- 512×256 pixels (131,072 total) with four colours: black, red, green and white. Pixel aspect ratio was appx. 0.667. This supported 25 lines of 85 characters. This has the designation 0.13M3.
The supported colours could be stippled in 2×2 blocks to simulate up to 256 colours, an effect which did not copy reliably on a TV especially over an RF connection.
Video Circuitry
Internally, the TV picture generation section of the ZX8301 IC operates in conjunction with the memory mapped picture display area to produce five signals suitable for driving a colour monitor. These signals, red, green and blue (RGB), CSYNCL (composite sync) and VSYNCH (vertical sync) are routed to an 8-pin DIN female connector. Certain issues of the ZX8301 are very fragile, and even unplugging the RGB connection whilst in use has been known to damage the IC.
Video Connectors
From the factory, the QL offers two video output connectors: RF and an 8-pin DIN connector with monochrome and colour composite output as well as the lines necessary for RGB.
A modification sometimes seen is a composite output tap cable, identified as a cable appearing from inside the computer with a coaxial cable terminated with a local connector e.g. in Belling-Lee connector in the UK.
SCART Cable
QL-to-SCART cables are available commercially. It is also possible to make a cable that works with your OSSC according to the following table. The QL pin numbers are per the QL User Guide / Concepts / Monitor diagram: be careful, there are multiple diagrams out there. Resistances are in series, and can be readily fitted inside the SCART connector. The resistances are necessary: the QL may be damaged if you have the RGB lines directly drive the low impedance (75 ohm) input expectations of the OSSC without the resistors. The SCART numbering assumes connection to a non-Japanese SCART (JP21), which used different connections.
| QL Name | QL Level | QL Pin | In-Line | SCART Pin | SCART Level | Impedance | Notes |
|---|---|---|---|---|---|---|---|
| RED | TTL | Pin 6 | 680 Ω | Pin 15 | 0.7 V | 75 Ω | Red |
| GREEN | TTL | Pin 8 | 680 Ω | Pin 11 | 0.7 V | 75 Ω | Green |
| BLUE | TTL | Pin 7 | 680 Ω | Pin 7 | 0.7 V | 75 Ω | Blue |
| VSYNC | TTL | Pin 4 | 10 Ω | Pin 16 | 1-3 V | 75 Ω | Using blanking signal to indicate RGB selection |
| CSYNC | /TTTL | Pin 3 | 1.2 kΩ | Pin 20 | 0.3 V sync | 75 Ω | Composite horizontal and vertical sync pulses provided via composite video input |
| GROUND | - | Pin 2 and shield | - | Pins 4, 5, 8, 13, 17, 18, 21 | - | - | Various grounds |
The 680 Ω resistors gets from TTL 5V to 0.7 Vpp. The 10 Ω resistor drops the 5 V to about 2 V, which is between the 1-3 V required to indicate RGB rather than composite 0-0.4 V. The 1.2 kΩ resistor drops the 5 V to about 0.3 V.
The OSSC does not require the SCART Status & Aspect Ratio up Pin 8 to be connected, unlike some older TVs which required 0 to 2 V → off, +5 to 8 V → on/16:9, +9.5 to 12 V → on/4:3.
The QL offers no readily accessible audio signal, so these connections simply ground the audio in the SCART connector.
OSSC-Specific Settings
The OSSC should be on AV1 (RGB-SCART) for the QL, as this input supports video in RGBS i.e. taking the RGB digital output from the QL and using its composite sync as a sync source.
OSSC-Experiments
Test equipment:
- A pre-Issue 6 QL.
- A RGB and sync cable as described above.
- OSCC V1.6 board (i.e. HDMI) with version 0.88a firmware.
- The input was identified as AV1_RGBS 312-p 15.62kHz 50.08Hz.
Preliminary experiments were with LineMult mode. The OSCC defaults to mode 1. It would seem mode 3 results in no cropping.
| LineMult | IMode Info | TV Resolution | TV Ratio | Notes |
|---|---|---|---|---|
| 1 | Preset 288p, IMode 312-p 50.08Hz, 539072/frame | 720x288@50Hz | 16:9 | Edges cropped |
| Line2x | Preset 288p, IMode 312-p 50.08Hz, 539073/frame | 720x576@50Hz | 4:3 | Bottom cropped |
| Line3x | Preset 960x288, 312-p, 539073/frame | 1280x864x50Hz | 4:3 | Image visible, horizontally compressed |
| Line4x | Preset 1280x288, IMode 312-p 50.08Hz, 539072/frame | 1280x1152@50Hz | 16:9 | Edges and bottom cropped |
| Line5x | Preset 1600x240L, IMode 312-p 50.08Hz, 539072/frame | 1080p | 16:9 | Top cropped |
Other Information
Inside the QL, the RGB and /CSYNC signals are also input to a RGB-to-PAL converter which produces composite PAL which was originally used to drive a domestic TV receiver. The same signals are mixed to produce a composite video signal to drive a standard monochrome monitor. When connected to a normally-adjusted TV or monitor, the video output would overscan horizontally. This was reputed to have been due to the timing constants in the ZX8301 chip being optimised for the flat-screen CRT display originally intended for the computer.
Further Reading
- Sinclair QL Wikipedia page
- QL with OSSC post at The QL Forum
External Links
- Dilwyn Jones's QL pages – Well maintained site with comprehensive QL related information.
- Repository of the Sinclair QL Preservation Project – Well maintained project with valuable Sinclair QL related information.
