smart-e 4K-RX9000, User Manual

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4K-9000 USER MANUAL V1.1
© 2018 Smart-e (UK) Ltd www.smart-e.co.uk PAGE | 42
19 TMDS DATA, CLOCK & COLOUR DEPTH
To understand the significance of the TMDS clock and how it can tell you a lot about the signal being
transmitted, first we must refer to the HDMI connector pin out as above. Pins 1-9 carry the three TMDS data
pairs, these cables are concerned with the transmission of video and audio information from source to screen.
Pins 10-12 are the TMDS clock pins, these pins provide the clock by which the data transmitted on pins 1-9 is
timed. In the case of HDMI 10 bits of data are transmitted per TMDS clock cycle. HDMI specification 1.4b to
which the 4K-9000 is compliant, supports a maximum clock rate of 340MHz or 340 million clock ticks per
second. We can from this show the maximum bandwidth throughput possible.
𝟏𝟎 𝒃𝒊𝒕𝒔 𝒙 𝟑𝟒𝟎𝑴𝑯𝒛 = 𝟑, 𝟒𝟎𝟎, 𝟎𝟎𝟎, 𝟎𝟎𝟎 𝒃𝒊𝒕𝒔 𝒑𝒆𝒓 𝒔𝒆𝒄𝒐𝒏𝒅 𝒐𝒓 𝟑. 𝟒𝑮𝒃𝒑𝒔 𝒑𝒆𝒓 𝑻𝑴𝑫𝑺 𝒑𝒂𝒊𝒓
𝟑. 𝟒𝑮𝒃𝒑𝒔 𝒙 𝟑 𝑻𝑴𝑫𝑺 𝑫𝒂𝒕𝒂 𝒑𝒂𝒊𝒓𝒔 = 𝟏𝟎. 𝟐𝑮𝑩𝒑𝒔 𝒕𝒐𝒕𝒂𝒍 𝒕𝒉𝒓𝒐𝒖𝒈𝒉𝒑𝒖𝒕
The clock is generated by the HDMI compliant source dependant on the amount of data being output, the
higher the resolution and colour depth, otherwise referred to as bits per pixel (bpp), the more bits need to be
transmitted and hence the TMDS clock speed must increase.
Colour depth or bits per pixel (bpp), define the number of colour information bits are transmitted per pixel of
video data. To be compliant with HDMI standards, all HDMI sources and screens must support 8-bit colour
depth, these 8-bits are per TMDS data channel, when a source is outputting in RGB mode these channels
represent the red, green and blue video data, so in total there are 8x3 = 24-bits per pixel of colour information.
Each 8-bit block of data is encoded to a 10-biy YMDS word. It is possible to send more colour information per
pixel, 10, 12 and 16-bit colour modes are available for sources and monitors supporting, what is referred to
as deep colour content. These modes give 30, 36 and 48-bpp respectively. Below shows the number of colours
possible dependant on the colour depth.
8-bit: 2^(8 x 3 TMDS channels) = 2^24 = 16.8 Million
10-bit: 2^(10 x 3 TMDS channels) = 2^30 = 1.07 Billion
12-bit: 2^(12 x 3 TMDS channels) = 2^36 = 68.7 Billion
16-bit: 2^(16 x 3 TMDS channels) = 2^48 = 281 Trillion