SERVICE MANUAL
Rev 1.0 21.10.02 16:23 Page 10
b. MPEG video decoder
This is a real-time video compression processor supporting the MPEG-1 and MPEG-2 standards at video rates up t
720 x 480 x 60 Hz and 720 x 576 x 50 Hz. Picture format conversion for display is performed by vertical and
horizontal filters. User-defined bitmaps can be super-imposed on the display picture by using the on-screen display
function. The display unit is part of the MPEG video decoder, it overlays the four display planes shown in the figure
below. The display planes are normally overlaid in the order illustrated, with the background color at the back and
the sub-picture at the front (used as a cursor plane). The sub-picture plane can alternatively be positioned between
the OSD and MPEG video planes where it can be used as a second on-screen display plane.
c. Audio decoder
The audio decoder accepts: Dolby Digital, MPEG-1 layers I, II and III, MPEG-2 layer II 6-channel, PCM, CDDA data
formats; MPEG2 PES streams for MPEG-2, MPEG-1, Dolby Digital, MP3, and Linear PCM (LPCM). The audio
decoder supports DTS® digital out (DVD DTS and CDDA DTS). SPDIF input data (IEC-60958 or IEC-61937
standards) is accepted if an external circuitry extracts the PCM clock from the stream. Skip frame, repeat blocks
and soft mute frame features can be used to synchronize audio and video data. PTS audio extraction is also
supported. The device outputs up to 6 channels of PCM data and appropriate clocks for external digital-to-analog
converters. Programmable downmix enables 1,2,3 or 4 channel outputs. Data can be output in either I²S format or
Sony format. The decoder can format output data according to IEC-60958 standard (for non compressed data: L/R
channels, 16, 18, 20 and 24-bits) or IEC-61937 standard (for compressed data), for FS = 96 kHz, 48 kHz, 44.1 kHz
or 32 kHz. Sampling frequencies of 96 kHz, 48 kHz, 44.1 kHz, 32 kHz and half sampling frequencies are supported.
A downsampling filter (96 kHz/48 kHz) is available. The decoder supports dual mode for MPEG and Dolby Digital. It
includes a Dolby surround compatible downmix and a ProLogic decoder. A pink noise generator enables the
accurate positioning of speakers for optimal surround sound setup. PCM beep tone is a special mode used for Set
Top Box. It generates a triangular signal of variable frequency and amplitude on the left and right channels. In
global mute mode, the decoder decodes the incoming bitstream normally but the PCM and SPDIF outputs are
softmuted. This mode is used to prepare a period of decoding mode, to synchronize audio and video data without
hearing the audio. Slow-forward and fast-forward trick modes are available for compressed and non-compressed
data. The control interface of the decoder is activated via memory mapped registers in the ST20 address space.
d. IR transmitter/receiver
The STi5518 provides a pulse-position modulated signal for automatic VCR programming by the set-top box. The
signal is output to the IR blast pin and an accessory jack pin, simultaneously. The pulse frequency, number of
pulses (envelope length) and the total cycle time is controlled by registers.
e. Modem analog front-end interface
The Modem Analog Front-end interface is used to transfer transmit and receive DAC and ADC samples between
the memory and an external modem analog front-end (MAFE), using a synchronous serial protocol. DMA is used to
transfer the sample data between memory buffers and the MAFE interface module, with separate transmit and
receive buffers and double buffering of the buffer pointers. FIFOs are used to take into account the access latency
to memory, in a worst case system and to allow the use of bursts for memory bandwidth efficiency improvement.
The V22 bis standard is supported.
f. Memory subsystem
On-chip
The on-chip memory includes 2Kbytes of instruction cache, 2Kbytes of data cache and 4Kbytes of SRAM that can
be optionally configured as data cache. The subsystem provides 240M/bytes of internal bandwidth, supporting
pipelined 2- cycle internal memory access. The instruction and data caches are direct-mapped, with a write-back
system for the data-cache. The caches support burst accesses to the external memories for refill and write-back.
Burst access increases the performance of pagemode DRAM memories.
Off-chip
There are two off-chip memory interfaces:
• The external memory interface (EMI) accessed by the ST20 is used for the transfer of data and programs
between the STi5518 and external peripherals, flash and additional SDRAM and DRAM.
