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by Nasta
Mon Dec 04, 2017 3:56 pm
Forum: Hardware
Topic: ULA ZX8301 - TV Picture Capabilities
Replies: 62
Views: 5373

Re: ULA ZX8301 - TV Picture Capabilities

It almost seems to make more sense to replicate the operation of the Aurora but in an FPGA that could be offered as a plug in replacement or plug in card ? You could design it from the get go for VGA / DVI / HDMI output. Exactly, and that is how Miracle's original Masterpiece graphics card started ...
by Nasta
Thu Nov 30, 2017 12:10 pm
Forum: Hardware
Topic: ULA ZX8301 - TV Picture Capabilities
Replies: 62
Views: 5373

Re: ULA ZX8301 - TV Picture Capabilities

I have also wondered how 68008 does read and write 16, and 32 byte entities over 8-bit data bus. No big mystery there - it's all explained in the 68000/8 user manual, it basically breaks larger transfers into a series of byte transfers, at least 4 clock cycles per transfer. That being said, because...
by Nasta
Thu Nov 30, 2017 1:23 am
Forum: Hardware
Topic: ULA ZX8301 - TV Picture Capabilities
Replies: 62
Views: 5373

Re: ULA ZX8301 - TV Picture Capabilities

with VSYNCH occuring at approximately line 288, if someone needs a precise number I'll re-measure this. Do you know at what point IPL1 is triggered? At the same time as VSYNCH? Not sure as this is done by the 8302 (it has a VSYNCH input for this), but I would assume at the rising edge of VSYNCH plu...
by Nasta
Wed Nov 29, 2017 8:50 pm
Forum: Hardware
Topic: ULA ZX8301 - TV Picture Capabilities
Replies: 62
Views: 5373

Re: ULA ZX8301 - TV Picture Capabilities

What could have been improved? Well, aside from the issue of using a 16MHz clock rather than 7.5HMz (which also has repercussions on the 8302 as the CPU clock is used for baud rate generation), the biggest improvement to be gained would have been handling the invisible vertical retrace period in a m...
by Nasta
Wed Nov 29, 2017 7:13 pm
Forum: Hardware
Topic: ULA ZX8301 - TV Picture Capabilities
Replies: 62
Views: 5373

Re: ULA ZX8301 - TV Picture Capabilities

The curse of issue 5 As stated before, the main difference between issue 5 and issue 6 boards is the HAL chip. However, on inspection, it does quite a bit more than just replacing a single 74LS03 chip. In fact, it also connects the 8302 directly to the CPU bus and decodes it instead of the 8301, lea...
by Nasta
Wed Nov 29, 2017 5:47 pm
Forum: Hardware
Topic: ULA ZX8301 - TV Picture Capabilities
Replies: 62
Views: 5373

Re: ULA ZX8301 - TV Picture Capabilities

DRAM refresh The 8301 relies solely on the pattern of screen reading to refresh the RAM, which is one reason it keeps 'fake reading' the screen even if the contents are invisible. DRAM is peculiar because it's data will self-destruct in a short time if it is not refreshed. This is because it is actu...
by Nasta
Wed Nov 29, 2017 4:28 pm
Forum: Hardware
Topic: ULA ZX8301 - TV Picture Capabilities
Replies: 62
Views: 5373

Re: ULA ZX8301 - TV Picture Capabilities

In detail: The 8301 operation is very much a slave of the process of picture generation. This repetitive process reads out the 32k of screen RAM as RGB pixels about 50 times a second, as a frame of lines of pixels. The process is based on CRT technology, but even the most modern monitors use a versi...
by Nasta
Wed Nov 29, 2017 2:40 pm
Forum: Hardware
Topic: ULA ZX8301 - TV Picture Capabilities
Replies: 62
Views: 5373

Re: ULA ZX8301 - TV Picture Capabilities

Results - the short version: The unexpected: It is quite possible that the 8301 and 8302 designs started life as a single large design, to be put into a larger chip. In particular the way the 8301 and 8301 are connected together on issue 5 boards and the way 8301 does decoding for 8302 and it's own ...
by Nasta
Wed Nov 29, 2017 1:49 pm
Forum: Hardware
Topic: ULA ZX8301 - TV Picture Capabilities
Replies: 62
Views: 5373

Re: ULA ZX8301 - TV Picture Capabilities

Preliminaries: How was it done? The following information has been gleaned from measurement rather than reverse-engineering the posted micro-photo of the 8301 chip, lest someone thought I'm some kind of reverse-engineering genius :) The 8301 does not do complicated things, as can be seen from the ac...
by Nasta
Tue Nov 28, 2017 9:17 am
Forum: Hardware
Topic: ULA ZX8301 - TV Picture Capabilities
Replies: 62
Views: 5373

Re: ULA ZX8301 - TV Picture Capabilities

Details of ZX8301 operation coming soon :)

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