Apple Technical Note HW 30 Sense Lines
Macintosh Technical Note HW 30, "Sense Lines" is a six-page Apple Developer Support note written by Rich Collyer and Blake Roberts in September 1992 and revised by Rich Kubota and Don Moccia in August 1994. It explains how Macintosh video hardware identifies the monitor connected to it from the three sense lines of the DB-15 video connector, and gives Apple's tables of sense codes.[1] Apple's Tech Info Library carried the same text, without the figures of wiring, as article 15987.[2]
Contents
[edit | edit source]- Sense lines and the original scheme (pp. 1-2): each line is read against pin 11 and is 0 when grounded and 1 when open, giving seven monitor codes and a "no display connected" code.[1]
- Extended type-7 codes (pp. 2-3): when no line is grounded the video hardware pulls each line low in turn and reads the other two. Figure 1 explains the six-bit notation, Figure 2 works an example, and Figure 3 draws the wire and diode connections for the PAL encoder, NTSC encoder, VGA and Super VGA, RGB 16-inch, PAL monitor and RGB 19-inch codes.[1]
- Extended type-6 codes (p. 4): sense line 0 grounded and lines 1 and 2 joined by a wire or by a diode in either direction, giving three multiple-scan monitor types (Figure 4). The Apple Multiple Scan 17 Display is sensed as a 16-inch multiple-scan type and the Multiple Scan 20 as a 21-inch type.[1]
- Table 1 (p. 5): the resolutions and frame rates that the Power Macintosh VRAM expansion cards support on multiple-scan monitors.[1]
- Summary (pp. 5-6): Table S-1, sense codes and frame rates; Table S-2, extended codes; Table S-3, DB-15 pin assignments. A worked example shows that joining pins 4 and 10 makes a PowerBook 180c detect a 16-inch RGB monitor, and that grounding them as well gives the 12-inch RGB code.[1]
What this note does not contain
[edit | edit source]It gives no cable or adapter part numbers and no pinouts for the HDI-45 or PowerBook video connectors. It names only a few computers and does not list which models recognise each code; Apple's support articles on the Quadra, Centris and multiple-scan displays cover that.[1]
Pages that cite this document
[edit | edit source]- Apple video cables and adapters: the DB-15 pin assignments, the original and extended sense code tables and the wiring of sense adapters.
Download: Apple Technical Note HW 30 Sense Lines.pdf
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Apple Computer, Macintosh Technical Note HW 30, "Sense Lines", Rich Collyer and Blake Roberts, revised by Rich Kubota and Don Moccia, August 1994, 6 pp. Hosted as File:Apple Technical Note HW 30 Sense Lines.pdf.
- ↑ Apple Computer, Tech Info Library article 15987, Macintosh Monitor Sense Codes: Technical Description (7/96), absurdengineering.org library. Based on Technical Note HW 30; Tables S-1, S-2 and S-3.