Search found 20 matches

by HGMuller
21 Sep 2018, 21:49
Forum: Hardware and software hacking
Topic: Extending the Gigatron instruction set
Replies: 22
Views: 2976

Re: Extending the Gigatron instruction set

This is indeed surprising. I was hooked on 2114 static NMOS RAMs (1K x 4), and the acces time I remember was 450ns! Hence I was happy if I could run at 2MHz. So I tend to look upon RAMs as very slow devices, and if I had to design something geared for speed, I would probably put the RAM on the faste...
by HGMuller
20 Sep 2018, 12:43
Forum: Hardware and software hacking
Topic: Extending the Gigatron instruction set
Replies: 22
Views: 2976

Re: Extending the Gigatron instruction set

Oops! :oops: I overlooked that the ACCU mode is not useless on the instructions that load X or Y, as the LD instruction passes the operand from the bus. LDX A, LDY A are the most obvious choice for transferring A to X or Y, so they are likely heavily used. There are plenty of alternatives, such as O...
by HGMuller
20 Sep 2018, 08:04
Forum: Hardware and software hacking
Topic: Extending the Gigatron instruction set
Replies: 22
Views: 2976

Re: Extending the Gigatron instruction set

Nice. Is the calculation for LS or HCT chips? Anyway, you can see that the RAM cannot start doing anything useful at all before 18 + 27 + 18 = 63ns into the cycle, as it isn't even fed the right address before that. And in the measurement this is even 86ns. The bus-mode decoder is not on the critica...
by HGMuller
19 Sep 2018, 20:10
Forum: Hardware and software hacking
Topic: Extending the Gigatron instruction set
Replies: 22
Views: 2976

Re: Extending the Gigatron instruction set

The point is that the data-valid time of from /OE of a RAM is usually much shorter than the 'access time' (which is data-valid from address-change or /CS). This is understandable from how the RAM works internally: an address change has to first propagate through the row decoder, then drive a row-ena...
by HGMuller
19 Sep 2018, 09:36
Forum: Hardware and software hacking
Topic: Extending the Gigatron instruction set
Replies: 22
Views: 2976

Re: Extending the Gigatron instruction set

What about something a little less intrusive? I'd hate to become incompatible with the current instruction set with all of the work people are doing developing the software. What if we just replace the instructions which are currently unusable? Specifically, the store instructions which write to RA...
by HGMuller
18 Sep 2018, 20:53
Forum: Hardware and software hacking
Topic: Extending the Gigatron instruction set
Replies: 22
Views: 2976

Re: Extending the Gigatron instruction set

Well, Y++ requires more than just a change of the control unit: you would have to replace Y by a counter. Of course allowing [X,D] also requires some fiddling with the data path, but these are just wire connections. It is true that my latest design abandoned the initial philosophy of making a 'compo...
by HGMuller
18 Sep 2018, 19:07
Forum: Hardware and software hacking
Topic: High resolution mode?
Replies: 32
Views: 3437

Re: High resolution mode?

It should be possible to symmetrize the signal presented to the mux select input by a circuit of some passive components: put a small capacitor between ground and that input, plus a pull-up resistor, and connect it through a (Schotky) diode to the clock source. The diode will discharge the capacitor...
by HGMuller
18 Sep 2018, 18:20
Forum: Hardware and software hacking
Topic: Audio storage of programs
Replies: 1
Views: 411

Re: Audio storage of programs

In the eighties I developed my own 6809-based computer. It also used audio tapes as storage medium, before I developed the controller card for a floppy disk. I had developed my own encoding system, which recorder at 1 KB/sec: the signal changed polarity 8000 times/sec ('clock transitions'), and for ...
by HGMuller
24 May 2018, 19:41
Forum: Hardware and software hacking
Topic: Extending the Gigatron instruction set
Replies: 22
Views: 2976

Re: Extending the Gigatron instruction set

Hookup a different type of output device so you don't need to worry about VGA signals (LCD or OLED display with I2C or SPI) Or a teletype! (Through 300 baud RS232.) Then you can use paper tape for permanent storage of programs. :o With RS232 you can also connect to the PC COM ports, an run a termin...
by HGMuller
24 May 2018, 17:56
Forum: Kit assembly gallery
Topic: Sockets for the ICs
Replies: 10
Views: 2258

Re: Sockets for the ICs

I always considered sockets a liability, which you only use as a last resort if it is absolutely mandatory the component is easily replacable. (Such as an EPROM that has to be taken out to be reprogrammed, or state-of-the-art memory chips, which sometimes might evelop a faulty bit.) It is just somet...