Some Markdown formatting fixes
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Jeff Parsons
Jeff Parsons
commit
29884d1ca5
1 changed files with 45 additions and 33 deletions
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@ -14,18 +14,18 @@ The combined contents of those ROMs have been stored as an 8Kb JSON image in [VT
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As Trammell Hudson's [VT100 Page](https://trmm.net/VT100) explains:
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There are four 8316E ROM chips for the 8080 CPU on the logic board. Since they are custom mask ROMs,
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Digital was able to have a different chip-select bit pattern and avoided having separate NOT gates on
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the inputs. Note that the schematic appears to be incorrect -- E56 is the low order, and E40 is the
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high order address bits.
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> There are four 8316E ROM chips for the 8080 CPU on the logic board. Since they are custom mask ROMs,
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Digital was able to have a different chip-select bit pattern and avoided having separate NOT gates on
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the inputs. Note that the schematic appears to be incorrect -- E56 is the low order, and E40 is the
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high order address bits.
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He then describes the memory map as follows:
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ROM chip CS1 (20) A11/CS2 (18) A12/CS3 (21) Mapped address
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E40 H H H 0x1800
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E45 H L H 0x1000
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E52 H H L 0x0800
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E56 H L L 0x0000
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ROM chip CS1 (20) A11/CS2 (18) A12/CS3 (21) Mapped address
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E40 H H H 0x1800
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E45 H L H 0x1000
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E52 H H L 0x0800
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E56 H L L 0x0000
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The above PCB chip locations correspond to the following [DEC ROMs](/devices/roms/dec/):
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@ -75,35 +75,47 @@ those characters to seamlessly connect with one another, so if the final bit in
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As page 4-52 of DEC's [VT100 Technical Manual (July 1982)](http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/terminal/vt100/EK-VT100-TM-003_VT100_Technical_Manual_Jul82.pdf)
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explains:
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Data, coming either from the screen RAM for scan 1 or the line buffer for scans 2 through 10, becomes part of an
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address to a character generator ROM. (See Figure 4-6-4, Character Generator Example.) The rest of the address comes
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from a scan counter in the DC012 control chip. The scan counter addresses the ROM according to which oftne ten scans
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is to be displayed. The 4-bit scan counter skips over the other 6 possible addresses to the ROM, so the ROM contains
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data in only 10 out of 16 locations. The output of the ROM is eight bits that represent the pattern of sequential
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dots to be displayed for that character on that scan. The eight bits enter the video shift register, a serializer
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that converts the eiight parallel bits into a one-bit-wide stream. An extra flip-flop stores the last bit so it can
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be output to the stream two or three extra times (depending on line length) to fill the intercharacter space.
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> Data, coming either from the screen RAM for scan 1 or the line buffer for scans 2 through 10, becomes part of an
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address to a character generator ROM. (See Figure 4-6-4, Character Generator Example.) The rest of the address comes
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from a scan counter in the DC012 control chip. The scan counter addresses the ROM according to which of the ten scans
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is to be displayed. The 4-bit scan counter skips over the other 6 possible addresses to the ROM, so the ROM contains
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data in only 10 out of 16 locations. The output of the ROM is eight bits that represent the pattern of sequential
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dots to be displayed for that character on that scan. The eight bits enter the video shift register, a serializer
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that converts the eight parallel bits into a one-bit-wide stream. An extra flip-flop stores the last bit so it can
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be output to the stream two or three extra times (depending on line length) to fill the intercharacter space.
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Also, VT100 circuitry includes a "Dot Stretcher" to make vertical lines appear as thick as horizontal lines. If you look
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at page 4-76 of DEC's [VT100 Technical Manual (July 1982)](http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/terminal/vt100/EK-VT100-TM-003_VT100_Technical_Manual_Jul82.pdf),
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you'll see the effect of the VT100's Dot Stretcher. Here's a copy of DEC's illustration:
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you'll see the effect of the VT100's Dot Stretcher. Here's how DEC illustrates it:
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20 dots for 2 characters ("Ap") in 80-col mode Actual characters displayed after dot stretching
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20 dots for 2 characters ("Ap") in 80-col mode
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0 . . . . . . . . . . . . . . . . . . . . 0 . . . . . . . . . . . . . . . . . . . .
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1 . . . . 1 . . . . . . . . . . . . . . . 1 . . . . 1 1 . . . . . . . . . . . . . .
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2 . . . 1 . 1 . . . . . . . . . . . . . . 2 . . . 1 1 1 1 . . . . . . . . . . . . .
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3 . . 1 . . . 1 . . . . 1 . 1 1 1 1 . . . 3 . . 1 1 . . 1 1 . . . 1 1 1 1 1 1 1 . .
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4 . 1 . . . . . 1 . . . 1 1 . . . . 1 . . 4 . 1 1 . . . . 1 1 . . 1 1 1 . . . 1 1 .
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5 . 1 1 1 1 1 1 1 . . . 1 1 . . . . 1 . . 5 . 1 1 1 1 1 1 1 1 . . 1 1 1 . . . 1 1 .
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6 . 1 . . . . . 1 . . . 1 . 1 1 1 1 . . . 6 . 1 1 . . . . 1 1 . . 1 1 1 1 1 1 1 . .
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7 . 1 . . . . . 1 . . . 1 . . . . . . . . 7 . 1 1 . . . . 1 1 . . 1 1 . . . . . . .
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8 . . . . . . . . . . . 1 . . . . . . . . 8 . . . . . . . . . . . 1 1 . . . . . . .
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9 . . . . . . . . . . . 1 . . . . . . . . 9 . . . . . . . . . . . 1 1 . . . . . . .
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0 . . . . . . . . . . . . . . . . . . . .
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1 . . . . 1 . . . . . . . . . . . . . . .
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2 . . . 1 . 1 . . . . . . . . . . . . . .
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3 . . 1 . . . 1 . . . . 1 . 1 1 1 1 . . .
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4 . 1 . . . . . 1 . . . 1 1 . . . . 1 . .
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5 . 1 1 1 1 1 1 1 . . . 1 1 . . . . 1 . .
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6 . 1 . . . . . 1 . . . 1 . 1 1 1 1 . . .
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7 . 1 . . . . . 1 . . . 1 . . . . . . . .
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8 . . . . . . . . . . . 1 . . . . . . . .
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9 . . . . . . . . . . . 1 . . . . . . . .
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The PC8080 [Video](/modules/pc8080/lib/video.js) function *createFontVariation()* takes both the "dot replication" and "dot stretching"
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features into account (along with other parameters, such as underlining and reverse video) when converting the character generator ROM data
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into fonts.
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Actual characters displayed after dot stretching
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0 . . . . . . . . . . . . . . . . . . . .
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1 . . . . 1 1 . . . . . . . . . . . . . .
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2 . . . 1 1 1 1 . . . . . . . . . . . . .
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3 . . 1 1 . . 1 1 . . . 1 1 1 1 1 1 1 . .
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4 . 1 1 . . . . 1 1 . . 1 1 1 . . . 1 1 .
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5 . 1 1 1 1 1 1 1 1 . . 1 1 1 . . . 1 1 .
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6 . 1 1 . . . . 1 1 . . 1 1 1 1 1 1 1 . .
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7 . 1 1 . . . . 1 1 . . 1 1 . . . . . . .
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8 . . . . . . . . . . . 1 1 . . . . . . .
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9 . . . . . . . . . . . 1 1 . . . . . . .
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The [PC8080 Video](/modules/pc8080/lib/video.js) *createFontVariation()* function takes both the "dot replication" and "dot stretching"
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features into account (along with underlining and reverse video parameters) when converting the character generator ROM data into fonts.
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### Disassembling the 8080 Firmware
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