ZR36050 datasheet(13/52 Pages) ETC

13 / 52 page

ZR36050

ADVANCE INFORMATION

QUANTIZATION AND HUFFMAN TABLES

The tables used by the ZR36050 to encode the image data are

always the ones that reside in the Quantization and Huffman

Table Stores. The host does not, however, write the table data

directly into these Table Stores, but in the Marker Segments

Section of Internal Memory. Therefore, before it can encode or

decode actual image data, the ZR36050 must first have preload-

ed the table data in the Table Stores.

In encoding, this can be done as part of the Statistical Pass or

Compression Pass (Baseline or Lossless), if the appropriate bits

of the MARKERS_EN register are set. Alternatively, it can be

accomplished as a separate operation, in the Tables Preload for

Encoding mode.

In decoding, if the marker segments preceding the compressed

image data contain table specifications, the ZR36050 decodes

these marker segments and preloads the tables in the Table

Stores, and decodes the image using these tables. Otherwise, it

uses the tables that pre-exist in the Table Stores, either decoded

from a previous image expansion, or preloaded using the Tables

Preload for Decoding operation.

Note that the same Huffman Table Store is used both in

encoding and decoding. However, the internal format of the

tables is different. Therefore, after a switch from encoding to

decoding, or vice versa, the Huffman Table Store is invalid, and

Huffman tables must be preloaded before image data can be

encoded or decoded. The Quantization Table Store remains

valid. In encoding, however, if the Scale Factor is changed, the

Quantization Table Store is clearly invalidated and must be pre-

loaded before the new Scale Factor can take effect.

NON-OPERATING STATES

The ZR36050 has four states in which it does not process data:

Idle, Waiting, Standby, and Freeze.

The host can access the Internal Memory in the Idle and Waiting

states, but not in the Standby and Freeze states.

Idle

The ZR36050 enters the Idle state after these events:

s de-activation of RESET

s activation of END at the end of an encoding or decoding

process

s abort of encoding, due to code volume overﬂow, or DCT

Coefﬁcient Buffer(s) overﬂow.

It remains Idle until the host issues the GO command (write to

address 0 of Internal Memory), to initiate a new encoding or

decoding process.

Waiting

In this state, the ZR36050 has stopped processing during

encoding or decoding, and is waiting for a response from the

host or system control circuitry in order to continue. It enters a

Waiting state in one of these conditions:

s INT is activated, i.e., a Status Register bit is set and the

corresponding Interrupt Request Register bit was enabled.

The ZR36050 continues processing after the host issues the

GO command.

s During encoding, if the DSYNC or EOS input signal is not

active together with the last sample of a block being input, the

ZR36050 ﬁnishes processing the current block and enters a

Waiting state. It resumes normal operation when DSYNC is

next activated.

Standby

When the device is in the Idle state, it can be switched to the

Standby state to conserve power, by activation of STDBY. In

Standby, if CLKEN is inactive, power consumption is further

reduced. After STDBY is deactivated, the host must wait at least

4 CLK_IN cycles before the first access to Internal Memory. After

reactivation of CLKEN, a recovery time of 5000 CLK_IN cycles

is required before any access is allowed. If RESET is activated

during Standby, the device will draw normal power as long as it

remains active.

Freeze

If the FREEZE input is activated, the ZR36050 freezes its oper-

ation by disabling the internal processing clock. It returns to

normal operation on the next CLK_IN after FREEZE is

deactivated.

ENCODING OPERATION

Figure 4 is an overview of the event sequence for typical opera-

tion of one of the encoding modes. The example shown is a

Compression Pass, with compressed data output in Master

mode via the Compressed Data Interface. For simplicity, the

example contains one scan, and the interrupt request is

assumed to be enabled only for the END status condition.

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