ICS2008B

4

ICS2008B Rev D 4/05/05

Functional Description

The following is a functional description of the hardware regis-

ters in the ICS2008B chip. It also describes how those

registers can be utilized by the software to facilitate specific

application services.

Hardware Environments

The ICS2008B operates as a peripheral to a processor such as

a PC or a single chip microprocessor. Many of the real time

requirements are satisfied by double buffering both incoming

and outgoing time codes.

LTC Input

LTCIN is a differential analog input feeding a comparator

with hysteresis. It requires capacitive coupling to the LTC

source. The output of the comparator goes to the LTC re-

ceiver, which is capable of receiving LTC in a forward or

frame rates. The incoming LTC data is sampled with a phase-

locked clock and loaded into the receive buffer following the

receipt of a valid LTC SYNC pattern. When a complete frame

has been received, an interrupt is generated.

LTC Output

The LTC output can be analog or digital. When set up as an

analog output, it can drive a high impedance load.

The LTC generator outputs a LTC frame at the selected frame

rate, such as 24 Hz, 25 Hz, 29.97 Hz or 30 Hz, and starts the

frame based on a start time generated by the selected LTC

SYNC source.

The output edge rate is programmable for SMPTE code (25

µsec) and EBU code (50 µsec) rise and fall times.

Video Inputs

There are two sets of video inputs. In a composite NTSC or

PAL system, the Y input is the only one used. It is capacitively

coupled to the source. In S-Video systems, capacitively couple

Y and C to their respective sources. Proper termination of the

source should be observed. Unused inputs may be left open.

One of the two video sources is selected by the VIDSEL bit in

the SMPTE control registers as the video SYNC source. Inter-

nal timers are synchronized with the incoming video to extract

timing information used to receive and generate VITC.

The VITC receiver samples the incoming video looking for a

valid VITC code on selected scan lines. When a valid code is

received it is written to a VITC receive buffer. More than one

line can contain VITC code, and the codes can be different. For

this reason, VITC codes from selected lines of a frame are writ-

ten to separate VITC buffers.

Video Output

The video output combines the selected video input with the

outputs from the VITC generator and the character generator.

It can be a composite or an S-Video output as selected by the

SVID bit in the SMPTE control registers.

VITC code is generated from data in the VITC generator

buffer and output during the selected line time(s). The CRC

and synchronizing bits are automatically generated by the

VITC generator, but all of the data fields are sent directly from

the buffer with no modification.

A character generator is provided to insert the time code in a

burn-in window which overlays the incoming video. The ver-

tical and horizontal position of the burn-in window is

programmable.

SMPTE SYNC Sources

A time code generator must have a SYNC input from a stable

source in order to position the LTC code properly on a audio

track of video tape or film. Three SYNC sources, video, click

input, and free running, are available. In the case of a video

tape, LTC code must start within plus or minus one line of the

beginning of line 5. This requires “Genlocking” to the incom-

ing video. The video timing section locks to the video’s

horizontal and vertical SYNC signal and generates a SMPTE

SYNC. If some external SYNC source is available it can be

input on the CLICK input. Otherwise, a free running SMPTE

SYNC is generated from the oscillator at the selected frame

rate.

Video Timing Generator

The video timing generator is “Genlocked” to the video

input’s SYNC separator. It extracts NTSC or PAL timing in-

formation from the video input and generates line and pixel

rate timing for the VITC receiver, VITC generator, LTC gen-

erator and character generator. If no video input is present, it

generates free running timing.

Overlay Character Generator

It is sometimes desirable to display the time code on a video

display along with the picture. A character generator is pro-

vided for that purpose. The time code display, or burn-in

window, can be positioned anywhere on the screen. It can be

displayed in two sizes with white or black characters on a

black, white or live video background.