GT 0x3b → Radio 0x68
0x45 is, for the best part, to manage when the radio is in the foreground, and to a lesser extent, how it behaves in the foreground.
It's ostensibly the GT equivalent of 0x20.
0x46Request Radio UI
# C23 BM
3B 04 68 45 00 12
3B 04 68 45 02 10
3B 04 68 45 03 11
# BM53
3B 04 68 45 0A 18
3B 04 68 45 0E 1C
Single byte bitfield.
PRIORITY = 0b0000_0001
AUDIO_OBC = 0b0000_0010
# Only applicable to MK3 (3-1/40+), MK4
NEW_UI = 0b0001_0000
NEW_UI_HIDE = 0b1000_0000
PRIORITY_RAD = 0
PRIORITY_GT = 1
When set to 1, the radio will still draw to display on user input i.e. changing radio station, but will relinquish the display after approx. 8 seconds.
When set to 0, the radio will remain in the foreground.
AUDIO_OBC_OFF = 0
AUDIO_OBC_ON = 1
When set to 1, the radio will relinquish the lower portion of the display that is otherwise allocated to menus.
The feature was removed with the introduction of the NG radios/updated UI.
The functional equivalence of the 8-bit bitfield between 0x45 and 0x46 suggests this bit might be better described as "only show header"
MK3 3-1/40+ and MK4 only!
Flag to signify the new UI that was introduced in ~2001 (3-1/40+).
I'm unaware of what effect this flag has. Allowing the radio to differentiate between the UI versions might suggest some degree of backwards compatibility- possibly related to the video module GT.
MK3 3-1/40+ and MK4 only!
This flag is set whenever BACKGROUND is set to 1, i.e. when MENU is pressed.
Like above, I'm not sure what effect this has.
A MENU button press does not get sent to radio, but is broadcast, and instead handled by the GT 0x3b, which will in turn, message the Radio 0x68, requesting it relegate itself to the background.
F0 04 FF 48 34 77 # MENU button press
3B 04 68 45 91 83 # GT (4-1/00) requesting radio relinquish foreground
68 04 3B 46 01 10 # Radio relinquishing foreground
The GT requesting the radio draw the radio UI at KL-R if the radio was on at ignition off
3B 04 68 45 00 12 # Request radio to foreground
For legacy GT, you may also see this with the Audio+OBC flag set (as per below).
3B 04 68 45 02 10 # Request radio to foreground (Audio+OBC enabled)
If the radio was not on at ignition off, and thus not on at KL-R, the radio will tell the GT that it is not writing to the display.
68 04 3B 46 01 10
The Audio and Onboard Computer (OBC) display "Audio+OBC" is a feature of the original UI, and allowed OBC data to be displayed alongside radio information.
Audio+OBC: The Video Module GT, and BM53 with the Audio+OBC feature enabled.
The feature is largely the responsibility of the radio, with the GT simply flagging whether the feature is turned on.
Ostensibly, if enabled, the radio just doesn't display menus during playback, thus not overwriting the lower portion of the display, which allows the OBC to remain in the foreground.
The value of this feature mightn't be inherently obvious in some regions.
Radios such as the C23 BM, and BM53 do not use menus, e.g. radio presets, CDC discs, thus this area of the display is essentially always blank in the absence of the OBC.
Video GT with C23 BM which does not use menus by default.