이름 : Osvaldo
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예식일 : 8 Ways Facebook Destroyed My Shield Control Cable Without Me Noticing
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Each of the 2K characters was represented by two bytes: a character byte, and an attribute byte. When the "plot" bit (bit 7) of the attribute byte was high, it indicated that instead of producing one of many 128 glyphs, the 8b of the character byte should be displayed instead as a 2x4 grid of fat pixels. The 8b parallel port was multiplexed with a bit of exterior logic as a way to scan the keyboard and to entry the inner floppy disk drive. The Compucolor design relied on LSI chips as a lot as possible in order to suit into the small cabinet at a reasonable value. With a purpose to see a coherent character, the same character and attribute bytes needed to be saved in corresponding positions of an excellent/odd row pair. The attribute byte acts as a sentinel to indicate the primary unused entry. When the "plot" bit (bit 7) of the attribute byte was low, it indicated that the character byte was to be interpreted in line with the table under. There is no reason why a couple of the I/O port ranges seem twice; it's simply incomplete decoding of the port address bus, saving a little bit of logic.

One obvious product was to put eight KB of RAM there, and another product put an socketed EPROM that filled that handle range, allowing storing numerous preloaded applications, reminiscent of an assembler and debugger. The empty eight KB vary at 0x4000 to 0x5FFF was put to use in various after-market products. It means the data stream may need lengthy-time period DC content material, but the recording medium is incapable of monitoring it; it additionally signifies that there are not any illegal bit encodings, such that there are no easy to distinguish encodings to make use of to sync to; it also signifies that the learn logic can't use AGC (automated gain management) and will need to have an absolute threshold for distinguishing a one bit from a zero bit. In one mode, the chip operated as meant, and drove the RS-232 serial port, permit the same old vary of hyperlink speeds (one hundred ten bps to 9600 bps) and cease bit choices. The other mode, described later, used an undocumented function of the chip to drive the floppy interface. Three would hearth, challenge an RST 3 instruction to the 8080. That routine would then drive one row of the keyboard, then read that parallel port to sense which keys linked to that row had been depressed.

Most different system have a tiny ROM routine to read a boot sector from the disk, which then loads in a 2nd level disk operating system, allowing for bug fixes and enhancements after the very fact. To deal with the first downside, the software blindly steps the r/w head out forty two times when it needs to dwelling the pinnacle to trace 0. The source code for FCS literally calls this the POUND routine. In the conventional handle range, the place the user is usually simply poking a byte at a time whereas typing or printing text, stalls the 8080 CPU till the horizontal blanking interval, at which point the video technology would not have to access RAM. The opposite address vary, 0x6000 to 0x6FFF, provides precedence to the CPU over video technology. One product even allowed stacking eight 8 KB banks into that one range, with software selection between which financial institution was energetic at any given time. If the CPU accesses the show RAM at the identical time the video generation logic does, the CPU wins and there is a visible "tear" within the video stream.

Because the show RAM is multiplexed between the video era circuitry and the need for CPU accesses, something should be achieved when both wish to entry video memory at the identical time. Aside from the scroll offset and the cursor addressing registers, the timing was set shortly after the CPU came out of reset, and the expectation was that it would not be written again. The chip additionally accepted an enter derived from the vertical sync timing of the video timing generator. Rather than having a self enough keyboard which used an somewhat costly LSI chip to map key presses to ASCII codes, the Compucolor instead would scan the keyboard itself. One benefit of this type of scanning is that for game play, it was doable to inform when a given key was depressed, held down, or released, not simply that it had been pressed. Not solely did this save expensive electronics, the coloration bandwidth was higher than NTSC would permit, resulting in crisper graphics than would have been attainable with modulation. Although it was essentially a personality oriented display (not bitmapped), it was possible to combine text of two completely different sizes with 128x128 graphics in eight different colours. There was no must module and demodulate the video sign: the graphics generator drove the CRT purple, green, and blue guns directly.

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