JVC 340 SC, 330, 370 SC service manual Working and Compressed Memory, Expanded Memory

Chapter 2—Functional Descriptions

As the CPU processes information, it is stored in the Working and Compressed Memory. This includes all temporary storage as well as the channel data that the operator sets while ‘tweeking up’ the projector.

All communication, both input and output, for internal signals and operator interface, is directly controlled by the processor. On-screen messages are generated and written to the Overlay Memory which serves as a video memory for controlling the on-screen display. RS-232 commands are received and sent via the RS-232 interface. IR communications are only received by the projector. No capability for transmitting IR is provided in the projector. The CPU communicates directly with the IR interface to receive commands. The CPU sends status and error codes to the LED interface for display on the dot-matrix display on the rear of the projector. Internal communication is accomplished by the processor sending data via the IIC interface and the serial data interface.

The CPU also directs the operation of the DSP.

Working and Compressed Memory

The Working and Compressed Memory (WCM) consists of four (4) SRAMs, mounted in sockets that provide battery backup which in turn provides the ability to maintain all projector settings even when the projector loses power for extended periods. Although not covered separately by warranty, the battery should be able to maintain the stored data for over one (1) year with no power applied to the projector. With power applied, the battery should remain viable for up to ten (10) years.

WCM is used as working memory for the CPU. All temporary storage of working data during routine CPU operations is done in the WCM. Additionally, the channel data is stored in WCM. There are 29 channels of data that can be stored in the projector. Channel data is all of the information that is stored that is specific to a particular projector channel. For example, the Position settings for R, G, and B, the ILA frequency, X convergence correction, Sensitivity correction, etc. As well as the channel data, global data is also stored in the WCM. This includes anything that is not channel specific such as auto-select groups, timers, and status logs. As long as the battery backup remains viable or power is applied to the projector, the WCM will remain intact. However, if data is corrupted for any reason, such as removing one (1) of the four (4) memory chips or a battery losing power while the projector is not plugged in, all of the data in the WCM will be lost. For this reason, it is always a good idea to back up the channel data to an external data storage medium.

Expanded Memory

The Expanded Memory (EXM) is composed of twelve (12) memories. Each of these memories stores information that will be used to correct the raster for both shading and convergence.

2-62 Model 330. 340SC, and 370SC Service Manual