The subsequent file appears immediately after that. The first file appears instantly after the final sector reserved for the listing entries, and is allocated contiguously. Slots in the directory table are absolutely packed and searched in order. The Compucolor design relied on LSI chips as much as attainable so as to fit into the small cabinet at a reasonable value. The 8b parallel port was multiplexed with a bit of external logic in order to scan the keyboard and to access the internal floppy disk drive. If the CPU accesses the show RAM at the identical time the video era logic does, the CPU wins and there is a seen "tear" within the video stream. Essentially the most modern a part of the Compucolor, as in comparison with most microcomputers of the identical time, was its colour display. This mode is used only when the ROM is clearing the screen, where 4 KB bytes should be written as shortly as potential, and slightly tearing shouldn't be an issue because the display is going to be displaying a solid shade anyway. Not only did this save pricey electronics, the color bandwidth was larger than NTSC would permit, shield control cable resulting in crisper graphics than would have been doable with modulation.
There was no need to module and demodulate the video signal: the graphics generator drove the CRT red, inexperienced, and blue guns straight. In one mode, the chip operated as meant, and drove the RS-232 serial port, allow the usual range of hyperlink speeds (a hundred and ten bps to 9600 bps) and stop bit options. One obvious product was to place 8 KB of RAM there, and another product put an socketed EPROM that filled that address range, permitting storing various preloaded packages, equivalent to an assembler and debugger. In the traditional address vary, the place the user is typically simply poking a byte at a time whereas typing or printing text, stalls the 8080 CPU until the horizontal blanking interval, at which point the video era doesn't have to entry RAM. FCS views the disk as four hundred sectors, sector 0 by way of sector 399. Sector 0 begins with a small descriptor indicating how many sectors are for use for the disk directory, and likewise comprises a 10 byte volume label. FCS (the File Control System) routines treat the disk as 400 sectors, quite than a monitor/sector addressing scheme. If the improper track/sector address is discovered, it merely waits for the following sector to return around and check out again.
If the incorrect observe/sector tackle is found, it merely waits for the subsequent sector to come back around and take a look at again. Once a gap is discovered, the ID block is learn. Once the suitable monitor and sector are discovered, the software program switches on the write enable and then writes the info block. One product even allowed stacking eight 8 KB banks into that one vary, with software choice between which bank was lively at any given time. Imagine having a one millisecond of no bit transitions then instantly getting a burst of 1s and 0s and having to decode them flawlessly; it's a troublesome problem. It also had a row offset register, allowing an environment friendly scrolling of the show without having to shuffle all of the bytes to effect the scroll. Rather than having a self ample keyboard which used an considerably expensive LSI chip to map key presses to ASCII codes, the Compucolor instead would scan the keyboard itself.
After scanning all the keyboard matrix, software would turn that into an prolonged ASCII code. CP/M did not have this and thus it was just a software convention to by some means sign the final significant byte of the file, eg -Z in a textual content file. If the software sees about five byte times of mark (1), it assumes it's an intersector gap and begins on the lookout for a begin bit. The attribute byte acts as a sentinel to point the primary unused entry. In observe, solely the first seven bytes have been used. Physical observe 1 is the primary logical observe. The 3-phase floppies had one step per observe, but the 4-part floppies had half the step size, requiring two steps per track. Note there is no such thing as a sensor for reporting track 0, and no write protect notch sensor. Alternatively, by putting all the FCS in ROM, there was no have to waste precious disk space on every floppy to hold it. Because the show RAM is multiplexed between the video era circuitry and the necessity for CPU accesses, something should be completed when each wish to entry video memory at the identical time. Most keys might produce 4 values, depending which combination of of the shift and control keys were pressed at the same time a daily key was struck.
Compucolor.org - Home
by Betty Callister (2025-01-22)
If the incorrect observe/sector tackle is found, it merely waits for the subsequent sector to come back around and take a look at again. Once a gap is discovered, the ID block is learn. Once the suitable monitor and sector are discovered, the software program switches on the write enable and then writes the info block. One product even allowed stacking eight 8 KB banks into that one vary, with software choice between which bank was lively at any given time. Imagine having a one millisecond of no bit transitions then instantly getting a burst of 1s and 0s and having to decode them flawlessly; it's a troublesome problem. It also had a row offset register, allowing an environment friendly scrolling of the show without having to shuffle all of the bytes to effect the scroll. Rather than having a self ample keyboard which used an considerably expensive LSI chip to map key presses to ASCII codes, the Compucolor instead would scan the keyboard itself.
After scanning all the keyboard matrix, software would turn that into an prolonged ASCII code. CP/M did not have this and thus it was just a software convention to by some means sign the final significant byte of the file, eg -Z in a textual content file. If the software sees about five byte times of mark (1), it assumes it's an intersector gap and begins on the lookout for a begin bit. The attribute byte acts as a sentinel to point the primary unused entry. In observe, solely the first seven bytes have been used. Physical observe 1 is the primary logical observe. The 3-phase floppies had one step per observe, but the 4-part floppies had half the step size, requiring two steps per track. Note there is no such thing as a sensor for reporting track 0, and no write protect notch sensor. Alternatively, by putting all the FCS in ROM, there was no have to waste precious disk space on every floppy to hold it. Because the show RAM is multiplexed between the video era circuitry and the necessity for CPU accesses, something should be completed when each wish to entry video memory at the identical time. Most keys might produce 4 values, depending which combination of of the shift and control keys were pressed at the same time a daily key was struck.