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Processor: Intel 8080 running at about 2.76MHz
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Basic display modes: 80x24 or 132x14 (132x24 for avo)
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RAM: 3KB(3072 bytes) combined screen and scratch
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ROM: 8KB(8192 bytes) for processor data and code ** ROMs include a checksum which is checked at self-test ** Checksum: every 2K, summed, mod 0xff == 0
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Character generation ROM(s): 2KB(2048 bytes) for characters
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Non-volatile RAM for storing configuration, ER1400 (1400 bits)
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AVO Option: 1K extra main RAM, 4K of FOUR BIT RAM for attributes.
Main Crystal: 24.8832 MHz NVR/LBA7: 15.734 kHz (63.556 uS); estimate at 8 * LBA4 LBA4 period : 7.945uS Even line: Kbd transmission time : 1.27mS/B Vertical freq: ~60 Hz Dot clock: 24 MHz in 132-char mode; 16 MHz in 80-char mode PSUART: 2.76480 MHz (Div9) Processor: 2.76480 MHz (Div9)
| Start | End | Size | Description |
|---|---|---|---|
| 0x0000 | 0x1fff | 8K | Basic ROM |
| 0x2000 | 0x2bff | 3K | Video and scratch RAM (see below) |
| 0x2c00 | 0x2fff | 1K | AVO - screen RAM |
| 0x3000 | 0x3fff | 4K | AVO - attribute RAM |
| 0x4000 | 0x7fff | 16K | Unassigned |
| 0x8000 | 0x9fff | 2Kx4 | AVO - program memory expansion ROM |
| 0xa000 | 0xbfff | 8K | AVO - program memory expansion ROM |
| 0xc000 | 0xffff | 16K | Unassigned |
ROM is four 2kx8 mask programmed ROMs. Main RAM is six 1kx4 static RAM chips. AVO RAM is another six 1kx4 static RAM chips.
Cleared out from 0x66 to 0xb9 -- 83 bytes At end of roms -- 1fd7 to 2000 -- 41 bytes
0x2004/0x2005 get saved and set to 70 03 when screensaver is on
| Start | End | Size | Description |
|---|---|---|---|
| 0x22c2 | 0x22c4 | 2B | SSvfl Vertical frames left until screensaver |
| 0x22c4 | 0x22c5 | 1B | SSbfl Vertical frames left until next brightness step down |
| 0x22c5 | 0x22c6 | 1B | SSst Screensaver state: 00 off, 01 fading, 02 on |
| 0x22c6 | 0x22c8 | 2B | SSprv Remember previous first line ptr |
| 0x22c8 | 0x22c9 | 1B | SSbrt Backup of brightness |
| Start | End | Size | Description |
|---|---|---|---|
| 0x2000 | 0x2012 | 18B | Blank lines for refresh (6 x 3B) |
| 0x2012 | 0x204e | 60B | Stack area (grows down from 0x204e) |
| 0x204f | 0x22d0 | 641B | Scratch Pad/Setup Area(?) |
| 0x2052 | 0x2054 | 2B | 0x2004 during init ? |
| 0x2068 | 0x2069 | 1B | Keys flag buffer |
| 0x206a | 0x206e | 3B | New keys pressed buffer |
| 0x20f6 | 0x20f8 | 2B | 0x22d0 during init? |
| 0x2014 | 0x2015 | 1B | 0xff during init? |
| 0x22d0 | 0x2c00 | 2352B | Screen RAM |
0x22bb through 0x22d0 appear to be unused!!!
We are using ??? as our screensaver counter.
Setup Area
| Start | Size | Description |
|---|---|---|
| 0x217b | 22 | Answerback message (20chars+2delim) |
| 0x2191 | 17 | Tabs (bit encoding) (first bit always set) |
| 0x21a2 | 1 | 80/132 col mode (00 = 80 col, 01 = 132 col) |
| 0x21a3 | 1 | intensity (00 = brightest, 0x1f = dimmest) |
| 0x21a4 | 1 | Mode byte for PUSART |
| 0x21a5 | 1 | Online/local |
| 0x21a6 | 1 | Switches 1 |
| 0x21a7 | 1 | Switches 2 |
| 0x21a8 | 1 | Switches 3 |
| 0x21a9 | 1 | Switches 4 |
| 0x21aa | 1 | Switches 5 |
| 0x21ab | 1 | TX baud rate |
| 0x21ac | 1 | RX baud rate |
| 0x21ad | 1 | parity |
| 0x21ae | 1 | nvr checksum |
Starts at 0x2000. Each line consists of a terminator (0x7f) followed by two bytes of address and attributes:
| 7 | 6 5 | 4 | 3 2 1 0 | 7 6 5 4 3 2 1 |
|---|---|---|---|---|
| S | AA | M | addr | addr |
S == 1 if part of scrolling region AA == 11 if normal atrributes M == 1 if ram starting at 0x2000, M = 0 if ram starting at 0x4000 (?) addr == low bits of address
| Location | R/W | Description |
|---|---|---|
| 0x00 | R/W | PUSART data bus |
| 0x01 | R/W | PUSART command port |
| 0x02 | W | Baud rate generator |
| 0x42 | W | Brightness D/A latch |
| 0x42 | R | Flags buffer |
| 0x62 | W | Non-volatile memory latch |
| 0x82 | W | Keyboard write |
| 0x82 | R | Keyboad read |
| 0xA2 | W | vid. proc. DC012 |
| 0xC2 | W | vid. proc. DC011 |
There is no even field mystery. It was the LBA 7 (also known as the NVR clock) all along!
data is D0 C1 is D1 C2 is D2 C3 is D3 !SPDS is D5
Accept address high, accept address low, standby, read, standby, (accept data is standby?) 22 23x9 22 23x9 0x2f 0x2d 0x2f 0x25 0x2f 0x30 0x23
| Bit | Active? | Description |
|---|---|---|
| 7 | H | KBD Transmit Buffer Empty |
| 6 | H | LBA 7(?) (It's a pin on the backplane connector...) - used to clock NVR - line buffer address |
| 5 | H | NVR DATA |
| 4 | L | EVEN FIELD (comes out of the video timing generator) |
| 3 | H | OPTION PRESENT (terminal output option???) |
| 2 | L | GRAPHICS FLAG (is VT52 graphics card present) |
| 1 | L | ADVANCED VIDEO (is AVO present) |
| 0 | H | XMIT FLAG |
| Location | Purpose |
|---|---|
| 0x00 | Startup |
| 0x08 | Keyboard interrupt |
| 0x10 | Receiver |
| 0x18 | Keyboard interrupt and receiver |
| 0x20 | Vertical frequency |
| 0x28 | Vertical frequency and keyboard interrupt |
| 0x30 | Vertical frequency and receiver |
| 0x38 | Vertical frequency and keyboard interrupt and receiver |
Other addresses are bitwise combinations of these interrupts! Crazy.
| Label | Description |
|---|---|
| X13de | add A to HL |
X1083 | set DE bytes starting at HL to B X02a4 | init: zero all RAM above stack X038b | memmov: copy B bytes from DE to HL X1083 | memset: set DE bytes starting at HL to B
Scans for characters in the FIFO in the control range (<0x20 or 0x7f).
8-bit data bus, 16-bit address bus. 8228 breaks devices on bus into write-only and bidirectional/read-only busses.
All value loads that could be addresses: X01c3: lxi h,X0815 ??? lxi h, 020e ??? right after loads keymapping table X0431: lxi b,X0113 (then call 0f7e,0e47) X05af: lxi h,X05b8 (then jmp a18) // Likely table? (but subsequent code at 5b8 is valid) X0c64: lxi h,X05ad (then jmp a18) // ... less likely table, feels like a chain X0c7a: lxi h,X0c8a (feels like a table)
This is an edge connector on the main board that contains breakout points for the RS232 and Modem lines. It can be used to disconnect the terminal from the normal serial port and connect it to an internal device. The external serial port is also available to the device as a plain connector.