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 as a substitute of generating one of the 128 glyphs, the 8b of the character byte ought to be displayed as a substitute as a 2x4 grid of fats pixels. The 8b parallel port was multiplexed with a little bit of exterior logic as a way to scan the keyboard and to access the interior floppy disk drive. The Compucolor design relied on LSI chips as much as potential in order to fit into the small cabinet at an affordable price. In order to see a coherent character, the identical character and attribute bytes needed to be saved in corresponding positions of a good/odd row pair. The attribute byte acts as a sentinel to point 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 accordance with the table beneath. There is no purpose why a couple of the I/O port ranges appear twice; it is just incomplete decoding of the port deal with bus, saving a little bit of logic.
One obvious product was to put eight KB of RAM there, and one other product put an socketed EPROM that filled that handle range, permitting storing varied preloaded programs, akin to an assembler and debugger. The empty 8 KB vary at 0x4000 to 0x5FFF was put to use in varied after-market products. It means the information stream might need lengthy-term DC content, but the recording medium is incapable of tracking it; it also signifies that there are not any unlawful bit encodings, such that there are no straightforward to differentiate encodings to use to sync to; it also means that the learn logic can't use AGC (computerized achieve 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 standard range of link speeds (110 bps to 9600 bps) and cease bit options. The opposite mode, described later, used an undocumented feature of the chip to drive the floppy interface. 3 would fire, issue an RST three instruction to the 8080. That routine would then drive one row of the keyboard, then read that parallel port to sense which keys connected 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 stage disk working system, permitting for bug fixes and enhancements after the very fact. To deal with the primary problem, the software blindly steps the r/w head out 42 instances when it wants to dwelling the head to trace 0. The supply code for FCS actually calls this the POUND routine. In the normal address vary, where the user is often simply poking a byte at a time while typing or printing textual content, stalls the 8080 CPU until the horizontal blanking interval, at which level the video generation would not need to entry RAM. The other deal with range, 0x6000 to 0x6FFF, provides priority to the CPU over video era. One product even allowed stacking eight 8 KB banks into that one vary, with software program selection between which bank was energetic at any given time. If the CPU accesses the display RAM at the identical time the video era logic does, the CPU wins and there is a visible "tear" in the video stream.
Because the show RAM is multiplexed between the video generation circuitry and the necessity for CPU accesses, something must be done when both want to access video memory at the same time. Except for 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 once more. The chip additionally accepted an input derived from the vertical sync timing of the video timing generator. Rather than having a self adequate keyboard which used an considerably expensive LSI chip to map key presses to ASCII codes, the Compucolor instead would scan the keyboard itself. One benefit of this style of scanning is that for sport play, it was possible to inform when a given key was depressed, held down, or released, not just that it had been pressed. Not solely did this save pricey electronics, the coloration bandwidth was higher than NTSC would permit, resulting in crisper graphics than would have been attainable with modulation. Although it was basically a character oriented display (not bitmapped), it was possible to combine text of two different sizes with 128x128 graphics in eight different colors. There was no need to module and demodulate the video sign: the graphics generator drove the CRT pink, inexperienced, and blue guns immediately.
If you have any kind of inquiries concerning where and how you can utilize shield control cable, you can call us at our web site.
10 Ways Facebook Destroyed My Shield Control Cable Without Me Noticing
by Raymond Munro (2025-01-21)
One obvious product was to put eight KB of RAM there, and one other product put an socketed EPROM that filled that handle range, permitting storing varied preloaded programs, akin to an assembler and debugger. The empty 8 KB vary at 0x4000 to 0x5FFF was put to use in varied after-market products. It means the information stream might need lengthy-term DC content, but the recording medium is incapable of tracking it; it also signifies that there are not any unlawful bit encodings, such that there are no straightforward to differentiate encodings to use to sync to; it also means that the learn logic can't use AGC (computerized achieve 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 standard range of link speeds (110 bps to 9600 bps) and cease bit options. The opposite mode, described later, used an undocumented feature of the chip to drive the floppy interface. 3 would fire, issue an RST three instruction to the 8080. That routine would then drive one row of the keyboard, then read that parallel port to sense which keys connected 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 stage disk working system, permitting for bug fixes and enhancements after the very fact. To deal with the primary problem, the software blindly steps the r/w head out 42 instances when it wants to dwelling the head to trace 0. The supply code for FCS actually calls this the POUND routine. In the normal address vary, where the user is often simply poking a byte at a time while typing or printing textual content, stalls the 8080 CPU until the horizontal blanking interval, at which level the video generation would not need to entry RAM. The other deal with range, 0x6000 to 0x6FFF, provides priority to the CPU over video era. One product even allowed stacking eight 8 KB banks into that one vary, with software program selection between which bank was energetic at any given time. If the CPU accesses the display RAM at the identical time the video era logic does, the CPU wins and there is a visible "tear" in the video stream.
Because the show RAM is multiplexed between the video generation circuitry and the necessity for CPU accesses, something must be done when both want to access video memory at the same time. Except for 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 once more. The chip additionally accepted an input derived from the vertical sync timing of the video timing generator. Rather than having a self adequate keyboard which used an considerably expensive LSI chip to map key presses to ASCII codes, the Compucolor instead would scan the keyboard itself. One benefit of this style of scanning is that for sport play, it was possible to inform when a given key was depressed, held down, or released, not just that it had been pressed. Not solely did this save pricey electronics, the coloration bandwidth was higher than NTSC would permit, resulting in crisper graphics than would have been attainable with modulation. Although it was basically a character oriented display (not bitmapped), it was possible to combine text of two different sizes with 128x128 graphics in eight different colors. There was no need to module and demodulate the video sign: the graphics generator drove the CRT pink, inexperienced, and blue guns immediately.
If you have any kind of inquiries concerning where and how you can utilize shield control cable, you can call us at our web site.