Top trace is the SETUP command received correctly.
The bottom trace is an example of the SETUP command at limit range.

RC5 Codes used on DP-500

Each command is 14 bits: SSTAAAAADDDDDD
Where SS = start bits: 11 or 10
T = Toggle bit (changes state with each new key press)
AAAAA = Device address: 11001
DDDDDD = Command data

RC5 works with a fixed bit rate where each bit period is divided into two halves of 889us, one half being a burst period of IR carrier (usually around 38KHz) and the other half being nothing (I'll call it a wait period). A logic 1 is a wait period followed by a burst, a logic 0 is a burst followed by a wait.

So, using the Standby command with Toggle=0 as an example, the full command would be: 11011001001100

Representing a 889us wait by _ and a 889us burst by X then we get:

_X_XX__X_XX_X__XX_X__X_XX_X_

Up Arrow with Toggle=1 would be 10111001 010110, thus:

_XX__X_X_XX_X__XX__XX__X_XX_

Don't worry too much about exact period timings or carrier frequency. I use 40KHz carrier, 875us burst (usually gets stretched a little by the IR receiver anyway) and a 900us wait period which comes very close to the 1778us bit period.

Codes with start bits = 11
Standby: 001100
0 to 9: 000000 - 001001
Play/Pause: 110101
Stop: 110110
Rewind: 110010
Fast Forward: 110100
Previous Chapter: 100001
Next Chapter: 100000
Clear: 101001
Eject: 101101
Step: 110000
Volume Down: 010001
Volume Up: 010000

Codes with start bits = 10
Up Arrow: 010110
Down Arrow: 010101
Left Arrow: 010001
Right Arrow: 010000
Enter: 010111
Title/Menu: 000010
Menu: 000011
Back: 001000
Zoom: 000100
Setup: 001010
Audio: 000101
SubPic: 000001
Angle: 001001
Repeat: 000000
Mark: 000110
Search: 001100