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ZR36050

JPEG IMAGE COMPRESSION PROCESSOR

Unspecified 

ADVANCE INFORMATION

ZR36050

registers, appends an EOI marker to the compressed data,

sets the END status bit, activates END, and goes into the Idle

state.

Statistical Pass

Operation of the Statistical Pass is similar to a Compression

Pass, except that the ZR36050 does not output compressed

data. If they are set, the APP, COM, DRI, DQT, DHT, and DNL

bits of the MARKERS_EN register are ignored in a Statistical

Pass. The OVF bit of the OPTIONS register is also ignored. A

Statistical Pass proceeds as follows:

s The ZR36050 processes the SOF marker segment, and sets

the RFM status bit.

s The ZR36050 processes the SOS marker for the first scan,

sets the RFD status bit, and deactivates STOP. The system

can then start supplying image data for the first scan.

s The ZR36050 processes the image data, until the EOS input

indicates the last data sample of the scan, and activates

STOP.

s If more that one scan is required, as indicated by the

OPTIONS register, the ZR36050 sets the RFM status bit and

processes the second scan.

s After the last scan, the ZR36050 computes the new Scale

Factor and the Allocation Factor.

s At the end of a stand-alone Statistical Pass, the ZR36050

writes the new Scale Factor, the Allocation Factor, the

Accumulated Code Volume, and the Total Activity in the

respective registers, sets the END status bit, activates END,

and goes into the Idle state.

If the Statistical Pass is part of an Auto Bit Rate Control op-

eration, the ZR36050 continues immediately with the Com-

pression Pass, using the new Scale Factor, and writes the

ACV_NET, ACT, and ACV_TRUN into their appropriate reg-

isters in the Internal Memory at the end of the Compression

Pass.

Tables-Only Pass

s The ZR36050 processes the SOF marker segment and any

of the DQT, DHT, APP, and COM optional marker segments

that are selected by the MARKERS_EN register. The

ZR36050 transfers the selected optional marker segments to

the compressed data after an SOI marker.

If an APP or COM segment is longer than 64 bytes, it can be

transferred by the means described for the Compression

Pass.

s The ZR36050 appends an EOI marker to the compressed

data, sets the END status bit, activates END, and goes into

the Idle state.

Tables Preload for Encoding

s The ZR36050 preloads the tables specified by the DQTI and

DHTI bits of the MARKERS_EN register. If DQTI is set, the

ZR36050 reads the quantization tables specified in the DQT

marker segment of the Internal Memory, multiplies them by

the Scale Factor, and stores them in the Quantization Table

Store. If DHTI is set, the ZR36050 decodes the Huffman

tables specified in the DHT segment of the Internal Memory,

and stores the decoded tables in the Huffman Table Store.

s It sets the END status bit and activates the END signal, and

goes into the Idle state.

DECODING OPERATION

Figure 5 is an overview of the event sequence for typical

decoding operation. The example shown is for full Expansion,

with compressed data input in DMA mode. For simplicity, a

single scan is shown and it is assumed that no interrupt request

is enabled.

A decoding operation starts as follows:

s Initially, after RESET is deactivated, the ZR36050 is in the

Idle state, awaiting the GO command, with the END and

STOP signal pins active. Alternatively, it could be in the Idle

state as a result of the completion of a previous operation.

s Before the host starts the ZR36050 by issuing a GO

command, the Control Registers must be initialized to their

appropriate states. If the registers are correctly configured

from a previous decoding operation, no action is required.

Otherwise, the host can write the initialization data in the

registers at any time while the device is in the Idle state.

s After the host issues the GO command, the ZR36050 clears

the END status bit, reads the Control Registers and initializes

itself for the selected operating mode and interface

configuration.

The continuation of the operating sequence from this point

depends on the operating mode selected.

When a status register bit becomes active, the ZR36050 contin-

ues processing unless the corresponding interrupt request

register bit was also set by the host. If it was set, the ZR36050

activates the INT output signal, stops processing and waits for

the host to intervene. INT is deactivated when the host reads the

status register, and the ZR36050 continues processing after the

host issues a GO command.

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