CRT Controller (CRTC). CONCEPT. The is a CRT Controller intended to provide capability for interfacing the / microprocessor families. A video display controller or VDC is an integrated circuit which is the main component in a . The Intel CRT controller was not used in any mainstream system, but was used in some S bus systems. The Motorola (MC) is a. Also, a memory known as display memory is required in the CRT to store the character data to be Intel. CRT. Controller. The INTEL

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A typical setup was as shown here in this picture. However it was not long until people started to look around for a smaller, simpler and quieter mode of data entry and display. Two modes of S video display were used. One utilized part of the CPU’s 64K memory address space to display text or graphics on a screen.

However this board was best suited for graphics rather than text. They allowed decent readable text to be displayed on a CRT monitor. However the text was limited to 64 characters per line, but they were fast — even for a 2MHz Some of the early video games were developed on these boards. The Sargon chess game with graphics was an early apex of this era. These specialized microprocessors put on one chip the ability to display text on a CRT monitor utilizing just a few support chips.

These dominated the S video display board systems in the end. There were and still are four popular CRT controller chips from that era. Let’s look at each briefly: Nonetheless, its operation was quite straightforward.

One reason for its relative simplicity of operation was that some of the functions that were user-programmable in other CRT controllers were mask-programmable in the DPs. Mask-programming of certain functions made a great deal of sense because, while many 827 need to be custom tailored to a particular design, they do not need to be altered once cotroller have been established.

The disadvantage of mask-programmable functions is, of course, that you must be a high-volume user of a particular programmed version of the DP in order to justify the cost involved. If you needed only a few devices and one of the standard pre-programmed versions cannot be used, you would not choose the The designers of th is chip had taken completely different approach to implementing the controller function.

While both the DP and devices allow you to specify many options, such as character size and timing chain parameters, the options are specified under program control instead of being mask-programmed as in the DP The unique feature of the CRT controller was the inclusion of two character buffers within the device.

The presence of these data buffers and the microprocessor interface logic provided by the imply, and in fact demand, a very specific system configuration — one that is quite different from that which would be used with the DP The device was usually used with a DMA controller such as a The DMA controller generated the screen memory addresses and loaded the data to be displayed into the ‘s “row buffers”. The cursor logic and blanking logic provided by the was quite extensive and allows you to easily implement a number of options with a minimum of external circuitry.

Light pen logic was contoller provided by the The Motorola The CRT controller was somewhere between the DP device and the device in its functional organization and capabilities. It was similar to the DP in the way that it was positioned functionally within a system; it coordinates the flow of data from screen memory to character generator logic and thence onto the CRT monitor, but data did not actually pass through the as was the case with the device.


However, the was a fully programmable contrroller, like theinstead of being contrpller like the DP The pro vided screen memory addressing logic but no memory contention logic.

The light pen logic, cursor logic, and scan line counters provided by the were similar to those of thealthough the scrolling and cursor logic was more limited in the Similarly, the blanking logic provided by the was minimal, although adequate, and did not provide as many options as the T he provided a full complement of programmable registers, there were however no status or control registers or signals provided by the to controler the microprocessor interface.

The functions provided by the may appear to be somewhat more elementary than those available with other above devices. Nonetheless, the still provided several interesting func tions not available on any of the above devices. If you compare this c hip to the other CRT controllers, it may appear that the amount of logic provided by the is approximately equal to that provided by the other devices. For example, controllet logic is provided by thebut the logic provided simply generates a continuous stream of dots at a specified cursor location.

You cannot make the cursor automatically blink, nor do you have any options in specifying the shape of the cursor symbol as was the case with the other CRT controllers. On the other hand, the SYNC generation logic provided by the exceeds that which is provided by most of the other devices. The provides no memory contention logic to simplify access to screen memory by both the microprocessor and the CRT controller.

Video display controller

It could not generate linear memory addresses. The NEC The video controller, which came out in the early 80’sbrought video display graphics to a new level. The “Graphics Display Controller” — as NEC called it, was an intelligent microprocessor peripheral designed to be the heart of a high performance raster-scan computer graphics and character display system.

Positioned between the video display memory and the microprocessor bus, the performed the tasks needed to generate the raster display and manage the display memory.

Processor software overhead was minimized by the ‘ s sophisticated instruction set, graphics figure drawing, and Cdt transfer capabilities. The display could be zoomed and pan ned, while partitioned screen areas could be independently scrolled. With its light pen input and multiple controller capability, the was ideal for advanced computer graphics applications. Unfortunately it never really caught on mainly because it was ahead of it’s time and there was a very steep learning curve to program the chip.

Also its color handling capability was limited. What Conrtoller controller should we use? 88275 all spend many hours these days looking at LCD displays with resolutions past x pixels per display, there is no reason why we should put up with a low resolution S video board. This will become more apparent when we go to 16 bit CPU systems next year. The microprocessor we decided upon two per board actuallywas the 32 bit, 8 core Parallax Inc. The Cogs each have their own local memory, and share access to the 32k Hub memory.

There are two types of RAM associated with this chip: A program running in a Cog whether a user program or the Propeller Spin Interpreter has access to the Hub RAM through the use of various word or byte instructions. The design of the Propeller is such that all of these 8725 are ‘atomic’, which means that they will always complete in full, never partially, and if two Cogs do write to the same Hub RAM location, the value placed will be that of the last written.


The value placed will never be a mix of what both Cogs attempted to write. The external EEPROM and cdt downloaded program must always contain a Spin program to be executed, even if this is just a small Spin program to place the Propeller in an operating mode other than as a Spin interpreter. This can be better understood when you realize that the Hub RAM does not contain primary machine code executed by the real processor as in conventional microcontrollers.

The Hub RAM contains just – data. The meaning of this data depends on what the real program s running in the COG s think is appropriate.

S Computers – Console IO Board

Cog RAM is the memory local to each Cog. It consists of longs of general purpose RAM for code and data, and 16 special purpose registers. BTW, the Propeller does not use interrupts as most other microcontrollers do. All external signaling events must be detected by polling or by waiting for an incoming line to go high or low. With the Propeller’s multi-Cog architecture this is not as much of a problem as it would be for a single core processor.

With one or more Cogs dedicated to ‘interrupt handling’, idling until the appropriate signal conditions are met, other Cogs can continue processing unaffected. It’s a different way of doing things. Once you get familiar with it turns out to be very efficient. Here is the classical diagram Parallax provides of their propeller chip: We will use the latter.

Video Output Each Cog has its own video generator module that facilitates transmitting video image data at a constant rate. Programming is fairly tricky requiring various registers to have carefully selected values. Fortunately there are a number of well written code examples available by now.

There is an almost religious following of people supporting this microprocessor.

The company Parallax has an outstanding reputation for support and help. With the extra space on the board we added a number of other useful functions. This allows you to tweak and optimize any code you write for the chip. Currently this can be done in two ways.

This is a small device that allows you to easily communicate with the Propeller over a USB port. It acts as an 8MB, high reliability, low power, fast and completely silent floppy disk drive! For this however we did have to add a second Propeller chip. There were simply not enough pins available on a single Propeller. The two boards communicate with a short over the top ribbon cable. More on this exciting addition later!

Here is an early picture of a partially built prototype Console IO board. As shown, it just collects keyboard characters and displays then on a VGA monitor.

Video display controller – Wikipedia

The red mini board is the Micro SD card Adaptor. Propeller0 is in the center of the board.

Here is an early schematic of this board. Here is a layout of the board. This was certainly the case with Spin written code but also so for Propeller driven assembly language code. Conroller eliminated the need for an S wait state requirement. Here is a picture of this second prototype board: A detailed schematic of this second prototype board can be obtained here.

Let us look at a few sections.

First the Keyboard Input section: They are set with switches SW2 and SW3.