For accessing the different components in computers you have to use the Address Bus. In most 8 bits computers there are 16 address lines.
The CPU on a 6502 can access 65536 addresses (16 bit ). But most chips in the circuit have just a few address lines. So the chip to use has to be selected using a CE (chip Enable) signal.
Old article i found on my fileserver from 1984
74 Series logic
Above example uses A15 combined with A14 to address the 16K ROM When using a 32k rom in the upper part of the memory, a15 can be used as CE
The 74ALS133 is a widely used decoder due to it’s many inputs.
Sometimes not all address lines are used for decoding, then you will get a repetition of the device in the memory map.
Above 6522 VIA has only 4 address lines RS0-RS3. But 2 chipselect pins (CS). If you connect the chip as below.
The chip would be selected when A15 is 1 and A14 is 0, A13-A04 it would not listen to. So its 4 bits addresses (total 16), would be repeated in a block $8000-$BFFF (10xx xxxx xxxx aaaa) 16384 addresses for 16 addresses on the 6522
ROM
Another simple solution to get a more precise address decoder without using a lot of components is using a ROM. But this wil only work for low speeds! A eeprom is relative cheap
Example ROM as chip enable/select
PAL PLA GAL
With these devices you can “program” a schematic which works as above example’s of the 74 series. But now you can do it using only one component.
PALs and PLAs are fuse-programmed, some are erasable like (e)eprom. Below a example of the code. Most of the PAL/PLA/GAL are hard to get and obsolete
;PALASM Design Description
;---------------------------------- Declaration Segment ------------
TITLE pRAM PC_interface Address Decoder
PATTERN pRAM97A.pds
REVISION H
AUTHOR Trevor Clarkson
COMPANY EEE KCL
DATE 30/05/97
CHIP decode PALCE20V8
;---------------------------------- PIN Declarations ---------------
PIN 1 AEN COMBINATORIAL ; INPUT
PIN 2 A9 COMBINATORIAL ; INPUT
PIN 3 A8 COMBINATORIAL ; INPUT
PIN 4 A7 COMBINATORIAL ; INPUT
PIN 5 A6 COMBINATORIAL ; INPUT
PIN 6 A5 COMBINATORIAL ; INPUT
PIN 7 A4 COMBINATORIAL ; INPUT
PIN 8 A3 COMBINATORIAL ; INPUT
PIN 9 A2 COMBINATORIAL ; INPUT
PIN 10 A1 COMBINATORIAL ; INPUT
PIN 11 IOW COMBINATORIAL ; INPUT
PIN 12 GND
PIN 13 IOR COMBINATORIAL ; INPUT
PIN 14 ACK_HALT COMBINATORIAL ; INPUT
PIN 15 PLS_EN COMBINATORIAL ; OUTPUT
PIN 16 BRDW COMBINATORIAL ; OUTPUT
PIN 17 MOD_CTRL COMBINATORIAL ; OUTPUT
PIN 18 RAM_ACCESS COMBINATORIAL ; OUTPUT
PIN 19 IO_16 COMBINATORIAL ; OUTPUT
PIN 20 LATCH_MOD COMBINATORIAL ; OUTPUT
PIN 21 LATCH_ADD COMBINATORIAL ; OUTPUT
PIN 22 P300 COMBINATORIAL ; OUTPUT
PIN 23 P300IN COMBINATORIAL ; INPUT
PIN 24 VCC
;PC address decoding functions (not all in this PAL)
;uses latched address to provide low-order address lines to pRAM/RAM
; A3 A2 A1 R/W Addr Function
; 0 0 0 R 300 MFF_0
; W not used
; 0 0 1 R 302 MFF_1
; W not used
; 0 1 0 R 304 MFF_2
; W not used
; 0 1 1 R 306 MFF_3
; W Latch Module Number
; 1 0 0 R 308 PLS_Status (pRAM status)
; W PLS_Control (pRAM control)
; 1 0 1 R 30A Weight/Connection-
; W Pointer RAM access
; 1 1 0 R 30C not used
; W Latched RAM address
; 1 1 1 R 30E not used
; W pRAM_256 module control
;
; NB. IO_16 must be tri-stated when not in use
;----------------------------------- Boolean Equation Segment ------
EQUATIONS
/P300 = A9*A8*/A7*/A6*/A5*/A4*/IOR + A9*A8*/A7*/A6*/A5*/A4*/IOW
/BRDW = /P300IN * /IOW
/PLS_EN = /P300IN*/A3*/IOR + /P300IN*A3*/A2*/A1
; MOD_CTRL is active HIGH
MOD_CTRL = ACK_HALT * /BRDW * A3 * A2 * A1 * /IOW
; RAM_ACCESS is active HIGH
RAM_ACCESS = ACK_HALT * /P300IN * A3 * /A2 * A1
IO_16 = GND
IO_16.TRST = /P300IN
; enable 16-bit transfers
; LATCH_MOD is active HIGH
LATCH_MOD = /BRDW * /A3 * A2 * A1
; LATCH_ADD is active HIGH
LATCH_ADD = /BRDW * A3 * A2 * /A1
;----------------------------------- Simulation Segment ------------
SIMULATION
TRACE_ON A9 A8 A7 A6 A5 A4 IOR /IOW /BRDW /PLS_EN MOD_CTRL RAM_ACCESS IO_16 LATCH_MOD LATCH_ADD ACK_HALT /P300 /P300IN
SETF /A9 /A8 /A7 /A6 /A5 /A4 /A3 /A2 /A1 IOR IOW /ACK_HALT /P300IN
SETF /IOW ; test P300 doesn't respond
SETF IOW /IOR ; test P300 doesn't respond
SETF IOR
SETF A9 A8 /A7 /A6 /A5 /A4 /IOR /P300IN
SETF A1
SETF A2 /A1
SETF A1 ; read mff0-3
SETF IOR /IOW ; test P300 and BRDW
SETF /A3 A2 A1 ; test Latch Module No
SETF IOW A3 A2 A1 ; MOD-CTRL not active until ACK_HALT
SETF ACK_HALT /IOW
SETF IOW /ACK_HALT
SETF A3 /A2 A1 ; check RAM_ACCESS
SETF ACK_HALT /IOW
SETF /ACK_HALT IOW
SETF ACK_HALT /IOR ; check READ and WRITE to RAM
SETF IOR P300IN
SETF /A3 A2 A1
SETF /ACK_HALT /P300IN
SETF IOW
SETF /A3 A2 A1 /IOW ; check LATCH_MOD
SETF IOW
SETF A3 A2 /A1
SETF /IOW ; check LATCH_ADD
SETF /A3 /A2 /A1 ; shouldn't happen normally
TRACE_OFF
;-------------------------------------------------------------------
FPGA
Example FPGA code. A solution which is too fancy for my 6502.
We are all getting older and electronics smaller. It’s hard to see if your soldering blobs are okay! Those blobs can reflect the light in a way that it’s not visible anymore to check them.
So i took Bigreds advice, and bought a G1200 Microscope. It’s a cheap but helpfull little gadget.
1-1200 times zoom
7inch screen (720p)
SDcard
Lipo battery
Recording on micro sdcard in 12 mega pixels pictures and 1080P Video. (even got a timer)
Focus button, and extra lights (There is a light source in de camera head, which can be adjusted by a knob)
When connecting to your pc, you get 3 options
PC Camera ( … so you can record using your pc with for example OBS)
Mass Storage, to read the SDCARD
Rec_mode ?!? – No idea yet
Below some examples:
Picture example
Video example
SDCard Access:
Access to the sdcard is a little hard. Connecting via Mass Storage is a solution. But i’ve put a little piece of tape to get the card in or out of the slot.
You can view the recordings on the Microscope itself. So i was wondering, can it play any other movie files?
I placed different MOV files on the sdcard, but the microscope skipped the ones i places on the sdcard myself.
I started to look at the metadata, and saw a Codec ID “qt 2016.04.21 (qt )”
mediainfo VID_001.MOV
General
Complete name : VID_001.MOV
Format : MPEG-4
Format profile : QuickTime
Codec ID : qt 2016.04.21 (qt )
File size : 551 MiB
Duration : 12s 0ms
Overall bit rate : 385 Mbps
Encoded date : UTC 1904-01-01 00:00:00
Tagged date : UTC 1904-01-01 00:00:00
Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : Main@L4.1
Format settings, CABAC : Yes
Format settings, ReFrames : 1 frame
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 12s 0ms
Source duration : 12s 360ms
Bit rate : 14.5 Mbps
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 25.000 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.280
Stream size : 20.8 MiB (4%)
Source stream size : 21.3 MiB (4%)
Language : 33
Encoded date : UTC 1904-01-01 00:00:00
Tagged date : UTC 1904-01-01 00:00:00
mdhd_Duration : 12000
Audio
ID : 2
Format : PCM
Format settings, Endianness : Little
Format settings, Sign : Signed
Codec ID : sowt
Duration : 12s 0ms
Source duration : 12s 288ms
Bit rate mode : Constant
Bit rate : 128 Kbps
Channel(s) : 1 channel
Channel positions : Front: C
Sampling rate : 8 000 Hz
Bit depth : 16 bits
Stream size : 188 KiB (0%)
Source stream size : 192 KiB (0%)
Language : 33
Default : Yes
Alternate group : 1
Encoded date : UTC 1904-01-01 00:00:00
Tagged date : UTC 1904-01-01 00:00:00
Tried to change this with ffmpeg, but it would not change the way i want.
ffmpeg -i VID_002.MOV -c copy -map 0 -brand 'qt 2016.04.21 (qt )' VID_007.MOV
mediainfo VID_007.MOV
General
Complete name : VID_007.MOV
Format : MPEG-4
Format profile : QuickTime
Codec ID : qt 0000.02 (qt ) <--------------- nope
Header of the movie clip maybe i have to look into this … later
I want to make a new clock module using a bare ATmega328 running on a 16mhz crystal. This to provide a clock for my 6502 computer.
Using a display and a rotary encoder I want to create a clock module which generates a 50/50 duty cycle clock 1Hz – 1 MHz.
Input module for my 6502 will be 5 buttons. (For now) that’s what’s left on the VIA on port A. (Rest is used by the display). The display i’m going to place directly on the bus. But I already ordered a second VIA. Matrix keyboard will be next. Then I will use the buttons in the picture for shift/alternate buttons. Because I’ll need about 25 keys. (See other posts) . I’ll probably end up making that one myself.
I found examples like this, rest i have to think of myself
{funny story] In 2019 i wanted to make a simple probe, which could detect 0 or 1 or a pulse. I wanted to make this on a little print using wirewrap wires and IC sockets. (I still have the tool which i used in the 90s.) When going to a well-known electronics shop in Den Hague. A great shop to get all kinds of oldskool electronics. But i’m getting ahead of the story. This shop has a lot of components for all kinds of electronics. New and what it looked like de-soldered component from boards or bought from old going-out-of-business shops or factories. Stuff you needed for 60s equipment. Well i was at the counter, asking a old guy. “Do you have wire-wrap wire” He said: ” No that’s old skool” …. {/funny story]
Latest wirewrap only a few years agoFrontToolsIn front the wirewrap sockets, I even had ZIF sockets (at the back) with long pins for wirewrapping.Ugly back from print
The wirewrap tool has a cable stripper. After stripping you would put a short part in the tool, place the tool over a IC pin and turning would wrap the wire on the pins. You could stack multiple connections on one pin. Removing could be done by turning the tool counterclockwise. Sometimes you had to remove the one closest to the print, replacing all wires. (Or cut the wrong/not needed wire and leave it in place … )
I’m thinking of moving my breadboard 6502 to a wirewrapped version. All my old boards are gone .. before i got a digital camera .. 🙁
Flashing ROMs .. (eeproms). It used to be a pain in the *$$. Burning took a looong time. But clearing one with UV took .. 20 minutes or so. Using one of these:
Altered clock module
Changed button press
Dipswitches for more speed control (red .. upper left)
Changed Rom/Ram
Changed addressing
Added RAM
ZIF Socket for ROM
VIC 6522
Fixed clock
Added buttons for interrupt
Display
Display works now
To test: Create Address logic to access display without VIA Can work, but not at high speed clock. Stays behind VIA
To buy: st7920 lcd 128×64
Generic improvements
Rewired most parts, using color codes (Blue data, Yellow Address and so on)
Added leds on data and address bus using ULN2803 darlington arrays
100nF Decoupling capacitors on the power rails
To do’s or ‘have to look into’s’
For sound i planned to use a General Instrument AY-3-8910, it is somewhere in my Lab, i know it is. I saved this chip and a SID for my Amiga addon soundcard. Where are my plans for the simple v1 setup? (FOUND IT)
I have to start writing rom functions for display usage. Like JSR $ff00 – Clear screen subroutine .. etc
I’m scraping information from websites, to get started on my clock controller. ATmega328 with ssd1306 display and rotary encoder/dip switches
Notes about the movie: Left side is Arduino IDE monitor reading Addressbus and Databus. (I’m going to try to rewrite this to realtime disassemble) Resetting system. Stepping CPU with manual clock pulses. Start vector being read at $FFFC/$FFFD. Program being run from $8000. Set clock on automatic ( ~ about 150 Hz ) Last opcodes you see a JMP loop 4C 2F 80, that is JMP $802F Display enlarged on video, was not visible on movie i took on mobile. (Wrong angle?)
Breadboard overview
Clock module
Reset module + Crystal
CPU + nmi/int buttons
RAM and ROM
Address decode + Bus divide
Addres/Data bus leds
6522 VIA + Display
2nd via + Buttons
?
(sound board)
TIL: 6502 can run without ram only rom,expect when using JSR … which uses a program stack in RAM
After a whole day soldering yesterday, ending up with a wire mess. Which didn’t work at the end…
Starting measuring some things, and create some test sketches (led blinky tests) I found out that the main problem was not having the red switches connected to GND. Blue switches where upside down, this was a easy fix. Because these are ON-ON switches, and where already connected to a common line. Then a mixup between D0 and D6 (wires crossed) And it is working! Made some lines and lettering on the frontplate after some playing around.
The Altair 8800 is a microcomputer designed in 1974 by MITS and based on the Intel 8080CPU. Interest grew quickly after it was featured on the cover of the January 1975 issue of Popular Electronics and was sold by mail order through advertisements there, in Radio-Electronics, and in other hobbyist magazines.
(picture from wikipedia)
UPDATE: 20220804 – Added Octal sheet
I alway loved the simple setup of this computer. There was no screen and no keyboard. Only later additions to the machine provided these.
One explanation of the Altair name, is that the name was inspired by Star Trek episode “Amok Time“, where the Enterprise crew went to Altair (Six).
There are only a few differences between the used 8080 CPU and the 8085 CPU of a machine i learned machinecode on.
See : https://www.henriaanstoot.nl/1989/01/01/8085-machinecode-at-school/
So for a really long time i wanted to have a Altair alike machine. There are do it yourself kits for sale. Which look like perfect relica’s and there are virtual machines and emulators. But i wanted to have the feeling of throwing the switches. You can find a emulator here (https://s2js.com/altair/)
So i bought the components, a poker case which can hold the machine. And started building today.
The backend is a arduino based emulator, but with real leds and switches! (https://create.arduino.cc/projecthub/david-hansel/arduino-altair-8800-simulator-3594a6)
Components and pokercaseDrillingFirst looks
Next to do:
Fix plate into case
Solder a LOT of wires and components!
Shall i get rid off the transitors and use darlington arrays?
Put lettering on the aluminium plate : Functions and Bus information.
Build a power connector in the case
And then … programming 🙂
UPDATE: 20220804 – Added Octal sheet
The Altair is a octal based machine, but i couldn’t find a opcode list in Octal. So i generated one. When entering a MOV D,M instruction for example, you have to enter x 0 1 0 1 0 1 1 0 using the switches Thats 126 in octal but most tables are in hex ( MOV D,M is 56, which is 0101 0110 but not that clear on the switches)
The workshop at MCH2022 gave me the idea to make my next PCB not at home, but professionally.
I’m planning to make my 6502 on modular PCB’s when i’ve got the base part working. ( I probably will only make THT (Though Hole Technology) boards instead of smd ) So i’ll probably end up making a few boards, namely:
Power on reset
Clock module
Interconnect with arduino
CPU, memory and ROM
Display
6522 Via
SID chip
Hex keyboard
This power-on reset is based on the original C64 part to reset the CPU when you power the machine on. With my 6502 i have to manually push reset to start booting. (The CPU starts in a unknown state when you power it up, it needs a reset)
MCH2022 is a nonprofit outdoor hacker camp taking place in Zeewolde, the Netherlands, July 22 to 26 2022. The event is organized for and by volunteers from the worldwide hacker community.
Knowledge sharing, technological advancement, experimentation, connecting with your hacker peers and hacking are some of the core values of this event.
MCH2022 is the successor of a string of similar events happening every four years since 1989. These are GHP, HEU, HIP, HAL, WTH, HAR, OHM and SHA.
I’ve bin to several of these big events. Besides these big events are many different smaller events (wannull, ne2000 etc).
First one i’ve been was HIP97. I went with Bigred at that time. I had to get the tickets at that time, he didn’t had a handle at that time. It was Monique who came up with his new nick.
After HIP97 there was HAL2001 WTH2005 and OHM2013 which i was present. HAL2001 the whole ICEcrew was present, WTH a part of them, OHM a few and i was with a few PRUTS friends.
Now i was with my girlfriend, AND with Bigred again! Loads of fun and memories. Had not seen Bigred since a inbetween hacker party at my place. So ’97 and now ’22 .. jeez 25 years!
So MCH, it was great again. Loads of stuff to do and to see. Weather was … okay. Two days where really hot, one day some light rain but a load of wind. Our neighbours tent collapsed, beer tents where reenforced. First campsite with a supermarket! Music stage was awesome, lasers and fire!
I went to a lot of talks, even my girlfriend found some she was interested in.
OpeningAt nightLast time my tapeTinkeringtar cz ourstuff.tgz
This was the last time i’ve brought my “Windows free zone tape” This big roll of tape was used on many occasions. I got this roll somewhere < 2000, I did a search but couldn’t find anything mentioning it on the web. Maybe some archive.org entry?
Starting a Home Computer Museum (which i almost did in the past)
streaming 360 video (going to try this with my Vuze XR Camera)
Non-Euclidean Doom: what happens to a game when pi is not 3.14159… (Really enjoyed this one)
Hacking the genome: how does it work, and should we?
And more
Besides the talks i’ve done some workshops:
Micropython on the badge (see my other post)
Kicad – PCB designing
Meanwhile we where looking at all the villages and hackerspaces. Loads of interesting people to meet. Like our neighbour two tents futher, he was also a home-brewer, and he brought a minifridge with beer taps connected to it.
When back at our tent or Bigreds Campervan, we talked about differences now and then. New technology, what we’ve been upto in the last years and tinkering, loads of tinkering.
I’ve brough a big plastic container with .. ehh “things to do ….”
My 6502, bigred helped me debugging the 16*2 display. (Luckily his campervan was packed with electronics!) We cannibalized one of his projects for a display, and re-flashed his eeprom programming arduino to test my display. ( The arduino i had to reflash later to program a rom he had given me for my 6502. ) Other toys he gave me: Print for the programmer, and a C64 Cartridge print for Exrom and Game.
Mini C64 with a little screen and raspberry zero.
5050 ledstrip (didn’t had time to reprogram this for our mood-light)
Handheld gamehat: Bigred found some old games he played when he was young
Mikrotik router, because i wanted to make a dmz for my girlfriends laptop. (MS)
Playing around with my Vuze XR camera
Huskycam, which i’m planning to use on a racetrack
DVB-T DAB FM Stick, got some hints and tips from Bigred. (Note to myself … fix the antenna!)
My Arduino touch bagpipe player with i2c
The wifi deauther, which has a display which i wanted to use to make a programmable clock for my 6502. Using a rotary encoder and the display to control the speed in Hz.
I spend many hours playing with the Badge and Kicad
Wrote some 6502 assembly, arduino sketches, php, bash and micropython.
While playing around with the badge i got some things working easily. Spinning logo and blinky leds. Next goal to achieve was, to get the gyroscope to control the angle of spinning. Most of the code worked, but the gyro values stayed zero! (After many hours …. you have to start/enable the chip/measurements on the bno055 first! .. duh! )
I didn’t had my dev directory from my main battlestation synced in my nextcloud, so changing things for the 6502 was a b*tch. Used vasm and acme to generate a bin file to use to fill the rom. Didn’t like the eeprom programmer program, because i could not easily check the rom contents. Have to look into that later on.
While learning to use Kicad, which i only had been using to draw schematics (besides fritzing) , i learned to create a pcb. Which gave me the idea to make a print for the power-on-reset for the 6502. Which is going to be the first PCB by ordering, instead of the old skool messing around with DIY print making. (see next post)
….. Oh, why my display was not working? I even connected my 8bit logic analyzer to the pins of the display.
Everything was correct. But i didn’t use a variable resistor for the contrast. Just a simple resistor i could find. Luckily … bigreds stash. All those hours debugging, all for one resistor! (I have to mention, we had a suspicion halfway. But it was too hot and we where too lazy to go to Bigred’s campervan, to get a potentiometer. )
Goodies from Bigred
"If something is worth doing, it's worth overdoing."