Download Print this page

Deramp Altair 8800c Manual

Front panel board set

Advertisement

Quick Links

Altair 8800c Front Panel Board Set
Introduction
The Altair 8800c front panel
board set is a drop-in re-
placement for the original Al-
tair 8800 front panel board.
The new board set was creat-
ed for the following reasons:
1) Availability
Finding an original front panel board to restore
or build an Altair is nearly impossible. The new
board set provides a drop-in equivalent that is
readily available.
2) Elimination of the Hand-Wired Harness
The original front panel board picked up bus sig-
nals and connected to the CPU board through a
large hand-wired harness. This harness was te-
dious to build and was often a reliability issue –
especially if you had to remove and work on the
front panel board. The 8800c board set replaces
the hand-wired harness with a 50 pin ribbon ca-
ble that connects to a bus interface board (shown here) to pick up and drive the required bus signals.
3) Mechanical Compatibility with the Altair 8800 Clone Cabinet
The original Altair 8800 cabinet made by Optima is no longer manufactured, and like the original
front panel board, finding an original cabinet by itself is nearly impossible. As an alternative, the cab-
inet for the Altair 8800 Clone is still available, however, the original front panel board covers mount-
ing points in the Clone cabinet's front panel bracket. This new front panel board is designed to fit
properly in the Clone cabinet's mounting bracket. The new front panel board also fits in an original
Altair cabinet.
4) Compatible with the 8800b CPU Board
The original front panel board does not work with an Altair 8800b CPU board and vice-versa. This is
due to a change in how the 8800b front panel injects data into the CPU and how it stops the CPU. For
increased flexibility, the new front panel set works with both the original and the 8800b CPU boards.
5) Logic Error Fixes
The original front panel board had a few logic problems that are fixed in the new front panel board
set. These same problems were also fixed by MITS when they designed the 8800b computer.
CPU "Stop" Timing Error
The Stop switch is designed to put the 8080 into a wait state on an instruction fetch bounda-
ry (the M1 cycle). However, due to a timing issue in the run/stop circuit, the front panel
doesn't always stop on an M1 cycle.
Ver 1.2, Feb 2019
Page 1

Advertisement

loading
Need help?

Need help?

Do you have a question about the Altair 8800c and is the answer not in the manual?

Questions and answers

Subscribe to Our Youtube Channel

Summary of Contents for Deramp Altair 8800c

  • Page 1 Altair 8800c Front Panel Board Set Ver 1.2, Feb 2019 Introduction The Altair 8800c front panel board set is a drop-in re- placement for the original Al- tair 8800 front panel board. The new board set was creat- ed for the following reasons:...
  • Page 2 Indeterminate Power-On State On power-on, the run/stop flip-flop on the front panel board is not initialized and the 8080 processor is not given a reset signal. These omissions tend to leave the 8080 in an invalid state on power-on. This is why the “STOP/RESET” switch sequence is required to put the computer into a valid state.
  • Page 3: Front Panel Board Assembly

    Front Panel Board Assembly Assembly of the front panel board is not a beginner’s project and these instructions won’t teach you how to solder components on a PCB, solder connectors, or show you the difference between a resistor and a diode. If you have any concerns about building this board, please contact me first. Many assembly details are illustrated in photographs that follow.
  • Page 4 Front Panel Assembly Steps First, insert and solder low-profile parts 1) Insert and solder R1-R52. 2) Insert and solder IC-A through IC-E (or sockets). 3) Insert and solder C1-C6. Note polarity on C6. The following instructions for installation of the switches and LEDs assume you have an Altair Clone cab- inet.
  • Page 5 5) Check that all switches are as squarely aligned as possible, then carefully lower the circuit board, component side down, onto the switches. Don’t let go of the board after you have it settled on the switches as the board will tend to rock towards you and fall off the switches. 6) To solder the switches, keep pressure on the board with your “spare”...
  • Page 6 2) Work the front dress panel over the switches and then down the switch bushings slightly. You don’t need to push the panel all the way down to the switch body. 3) Turn the PCB/front panel over as shown below and let the LEDs fall into the front panel LED holes. If the front panel sags a bit in the middle, add a third support point near the middle of the panel.
  • Page 7 Lastly, install J1 and J2 on the back side of the circuit board. J1 – Note the orientation of the keying slot before soldering the connector onto the board. Again, the connector goes on the back side of the board. J2 –...
  • Page 8 Final Assembly (using an Altair Clone cabinet) Mount the circuit board to the front panel support bracket. 1) Set all toggle switches in the down position. Feed the switch batons into the holes through the rear of the sup- port bracket. Be sure the bracket is fully seated against the body of every switch.
  • Page 9 Mount the front dress panel to the front panel sup- port bracket. 1) Slide a 0.150 white spacer over each of the six studs on the back of the front dress panel. 2) Insert the batons from the switches into the front panel and work the studs into the holes on the front panel support bracket until the front panel and support bracket have fully sand-...
  • Page 10 Install the Front Panel Assembly into the Case. 1) Slide the front panel assembly in from the front of the case. The front panel may be snug as it goes into the case bezel. If this is the case, work the panel in bit-by-bit, keeping the amount of insertion on all four sides approximately equal as you work the panel backwards into place (where the mounting bracket’s threaded holes line up with the four holes in the bottom of the case).
  • Page 11 Interface Board Assembly Assembly of the interface board is fairly straight forward, however, these instructions won’t teach you how to solder components on a PCB, solder connectors, or show you the difference between a resistor and a diode. If you have any concerns about building this board, please contact me first. Parts List (interface board) Designator Description Part Number...
  • Page 12 Interface Board Assembly Steps Insert and solder parts working from shortest to tallest: 1) Insert and solder R1-R6 and D1 (or wire jumper – see * above) 2) Insert and solder VR1. Bend the leads such that the hole in the mounting tab lines up with hole in the circuit board.
  • Page 13: Power Supply Note

    Altair 8800c Computer Assembly Hints Grounding For maximum resistance to static shock, make sure all sections of the metal cabinet are in electrical con- tact with each and with the power supply enclosures. Then also ensure the power cord ground wire is connected to the chassis ground terminal on each of the power supplies.
  • Page 14: Front Panel Operation

    Front Panel Operation In its default configuration, the 8800c Front Panel board set duplicates the operation of the original Al- tair front panel. In addition, the following features can be selectively enabled as desired: • Power-on to a valid reset state •...
  • Page 15 ever the computer is stopped. The output latch is displayed only while the AUX-Right switch is held down – normal display is restored as soon as the switch is released. The output latch feature is controlled by VDIP #1, bit 6. A value of 1 turns on the output latch, a value of 0 turns off the output latch.
  • Page 16 Quickly toggle the switch, don't leave the switch in the up position. Before starting, make sure all the switches are in the down position. See http://deramp.com/downloads/altair/software/miscellaneous/ Pong PONG for Altair front panel. Left player quickly toggles A15 to hit the "ball." Right player toggles A8.
  • Page 17 Power-On and Reset Auto-Jump The front panel can force an auto-jump upon power-on and/or reset. The auto-jump address can be dif- ferent for power-on than for reset. This is unlike many auto-jump circuits which perform the same ac- tion for power-on and for reset. For Altair BASIC and Altair DOS, duplicate auto-jump addresses can be problematic.
  • Page 18: Firmware Updates

    Firmware Updates The logic on the front panel and interface boards is controlled by a state machine in a PIC16F1828 pro- cessor. The firmware in the processor can be updated while the board set is installed in a working Altair computer.
  • Page 24 State Machine Signals Port Name Description smCYCLE* Low to start a single 8080 machine cycle. Must hold low at least 500ns to ensure phi2 edge has occurred. Must return high within 1500ns max. Recommend 750ns low to cycle the processor one cycle. smRESET High to assert bus PRESET* signal (processor reset).
  • Page 25 50 Pin Ribbon Cable to Front Panel Signal Signal SERCLK INLAT SERIN WAIT HLDA INTE PROT MEMR HLTA STACK...
  • Page 26: Front Panel Interface

    IC Utilization Front Panel Interface Gates IC's Designator 74LS02 Quad 2-Input NOR 3/4 of G used 74LS00 Quad 2-Input NAND 74LS10 Triple 3-Input NAND 1/3 of K used 74LS30 Single 8-Input NAND 74LS04 Hex Inverter 5/6 of M used 74LS368 Hex Bus Driver 74LS109 Dual J-K* Flip Flop E, F 74LS374 Octal Latch...
  • Page 27 Altair Bus Signals Signal Description Signal Description +18v -18v XRDY Another RDY signal OR'd to 8080 SSWDSB* Direct sense switch input to the processor VI0* Vectored interrupts 0-7 EXTCLR* Return all slave boards to known state VI1* 60hz for Real-Time Clock VI2* STSTB* Status strobe...
  • Page 28 Altair Clone Case For shipping purposes, the Altair Clone enclosure has been assembled. To install items into the case, the top of the case and the front panel assembly (dress panel and bracket) must be removed and disassem- bled. Save all screws, nuts and spacers as you disassemble these items. 1) Remove the two screws towards the rear of the case cover that hold the cover in place.