EDID decoding on the Mac, to find out what resolutions and rates the Mac is seeing reported.

edid-decode source URL

http://cgit.freedesktop.org/xorg/app/edid-decode/plain/edid-decode.c

compile with:
gcc edid-decode.c -o edid-decode

get EDID from IORegistryExplorer (mine, an old 24" Apple Cinema Display, is attached).

Convert to binary with this command:
ruby -e 'File.open("edid", "wb").write(File.read("edid.txt").split.map { |s| ("0x"+s).to_i(16) }.inject("", "<<"))'

Decode your EDID with this command:
./edid-decode edid

My output is attached.

edid.txt

00 ff ff ff ff ff ff 00 06 10 1c 92 de ce 00 02
15 11 01 03 80 31 1f 78 2e fd 45 a3 57 4a 9e 25
13 50 54 00 00 00 d1 00 01 01 01 01 01 01 01 01
01 01 01 01 01 01 28 3c 80 a0 70 b0 23 40 30 20
36 00 ef 36 11 00 00 1a 00 00 00 ff 00 32 41 37
32 31 33 4a 4e 58 4d 4e 0a 20 00 00 00 fc 00 43
69 6e 65 6d 61 20 48 44 0a 20 20 20 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 e4
40 01 02 00 00 00 00 7e 24 01 a5 00 ff ff 03 1a
1a a8 01 00 00 00 00 00 40 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 57

gistfile3.txt

Extracted contents:
header:          00 ff ff ff ff ff ff 00
serial number:   06 10 1c 92 de ce 00 02 15 11
version:         01 03
basic params:    80 31 1f 78 2e
chroma info:     fd 45 a3 57 4a 9e 25 13 50 54
established:     00 00 00
standard:        d1 00 01 01 01 01 01 01 01 01 01 01 01 01 01 01
descriptor 1:    28 3c 80 a0 70 b0 23 40 30 20 36 00 ef 36 11 00 00 1a
descriptor 2:    00 00 00 ff 00 32 41 37 32 31 33 4a 4e 58 4d 4e 0a 20
descriptor 3:    00 00 00 fc 00 43 69 6e 65 6d 61 20 48 44 0a 20 20 20
descriptor 4:    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
extensions:      01
checksum:        e4

Manufacturer: APP Model 921c Serial Number 33607390
Made week 21 of 2007
EDID version: 1.3
Digital display
Maximum image size: 49 cm x 31 cm
Gamma: 2.20
DPMS levels: Off
Supported color formats: RGB 4:4:4, YCrCb 4:2:2
Default (sRGB) color space is primary color space
First detailed timing is preferred timing
Established timings supported:
Standard timings supported:
  1920x1200@60Hz
Detailed mode: Clock 154.000 MHz, 495 mm x 310 mm
               1920 1968 2000 2080 hborder 0
               1200 1203 1209 1235 vborder 0
               +hsync -vsync
Serial number: 2A7213JNXMN
 Monitor name: Cinema HD
   Manufacturer-specified data, tag 0
Has 1 extension blocks
Checksum: 0xe4

DI extension block

EDID block does NOT conform to EDID 1.3!
	Digital display field contains garbage: 1
	Missing monitor ranges

The new link is https://git.linuxtv.org/edid-decode.git/, with mirror at https://github.com/timvideos/edid-decode