8-bit printer on Plus

Started by arnoldemu, 18:02, 20 January 10

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

arnoldemu

In the Plus schematics it says to make a link on the pcb to enable the 8-bit printer port on the Plus. The 8th bit is then controlled by bit 3 of register 12 in the emulated 6845.

Does anyone know if the Plus was shipped with this link made or not made?
My games. My Games
My website with coding examples: Unofficial Amstrad WWW Resource

Grim

The 6128Plus schematic says to fit R130 for 8bit printer. This resistor (it's not a link) is connected to pin9 of IC108 (a 74HC4051). Now looking at the PCB, there's no R130 and IC108 on it, it seems they got the labels wrong :)

However, you can easily spot the 74HC chip (IC8 on the PCB) and find out that R30 is the R130 the schematic is talking about. I've attached a picture taken from my 6128Plus which shows that the resistor is actually fitted by default.

No idea what really happens if it is removed tho.

Bryce

#2
Looking at the schematics, R130 seems to be just a pull-down resistor for the signal between the gate array and analogue multiplexer. In the 6128plus, the gate array has mux0/1/2, which are outputs it can use to select which analogue source it wants to read, the 4051 has 8 analogue inputs, using the 3-bit port you can select which one gets switched through to the output (pin3) which in turn gets fed through the LA6393, unfortunately Amstrad chose not to use an ADC which would have given the analogue input a decent resolution that you could do something with, instead they chose a comparator, this means that the joystick (although analogue) is still only being read as 1 bit, ie: the bit changes from 0 to one as the joystick passes it's centre point. Pretty pointless calling it analogue really.

But as far as selecting whether the printer port is 7 or 8 bit (or the other options associated with R128/129), Amstrad obviously uses mux0/1/2 as option inputs at boot up. Possibly the pull-downs aren't actually required for the analogue selection signals, but also don't effect it's function and also can be used to select certain configurations within the gate array.
Just a sneaky way of making the most use of your physical i/o pins, which in turn reduces cost.

Removing R130 would probably just cause PR7 (Pin 154) to always stay low, ie: the printer port is now only 7 bit just as all non-plus printer ports were. Can't really see any use in down grading though. Maybe they kept the option because of some printer or expansion in-compatibility.

Bryce.

TFM

Quote from: arnoldemu on 18:02, 20 January 10
Does anyone know if the Plus was shipped with this link made or not made?

I can only tell you that my CPC Plus is able to print 8 bit characters to my printer, without any modification. So the default is: Printer is working!

Sure, you have to use a routine using the CRTC address to set the 8. bit!

TFM of FutureSoft
Also visit the CPC and Plus users favorite OS: FutureOS - The Revolution on CPC6128 and 6128Plus

TFM

Quote from: Bryce on 22:05, 20 January 10
.... unfortunately Amstrad chose not to use an ADC which would have given the analogue input a decent resolution that you could do something with, instead they chose a comparator, this means that the joystick (although analogue) is still only being read as 1 bit, ie: the bit changes from 0 to one as the joystick passes it's centre point. Pretty pointless calling it analogue really. ...
Bryce.

Hi, I'm not sure if I understand you properly, but the analogue joystick of the CPC Plus works indeed with analogue values. I only have a cheap analogue joystick, and I can read analogue values in X and Y between 0 and 63 (means 6 Bits count!). So I can't talk about a third axis...
It's pretty simple to use the analogue joystick of the CPC Plus. For example the Plus version of FutureOS supports the analogue joystick, there you can see how well it works.
TFM of FutureSoft
Also visit the CPC and Plus users favorite OS: FutureOS - The Revolution on CPC6128 and 6128Plus

Bryce

Ah ok. I only took a quick look at the schematic yesterday (and have no practical experience using a real CPC+) and assummed that the gate array only had digital inputs, but obviously the COMP input (Pin 15) is analogue and is being compared with the ADC0/5 pins to give a 6 Bit ADC resolution and the comparator (LA6393) is just being used to scale the input value from the joystick. Electronically it's quite a strange method of solving the ADC conversion, but I'm sure they had their reasons to do it this way.

Bryce.

arnoldemu

Quote from: TFM/FS on 23:37, 20 January 10
I can only tell you that my CPC Plus is able to print 8 bit characters to my printer, without any modification. So the default is: Printer is working!

Sure, you have to use a routine using the CRTC address to set the 8. bit!
Great thanks. I have been loocking over the CPC, Plus, KC Compact and Aleste schematics and fixing bugs in Arnold.

The same goes for my question about 50/60Hz. The link is there on the pcb to define it.

I am working on Arnold and soon there will be a release with aleste emulation and lots of bug fixes.
My games. My Games
My website with coding examples: Unofficial Amstrad WWW Resource

TFM

Quote from: arnoldemu on 12:20, 21 January 10
The same goes for my question about 50/60Hz. The link is there on the pcb to define it.

On the CPC oG (old generation) there is a wire (soldered or cut) that defines 50/60 Hz. But in effect the OS reads a bit from the PIO that ist set or cleared, then the OS switches to 50 / 60 Hz. It's similar to the name-selection of the CPCs.

For the CPC Plus... I didn't find the same hardware structure. I tried to set some connections and to cut some connections on the BASIC cartridge, but I was not able to change the manufacturer name or the 50/60 Hz state. There may be a hidden switch. But I dont't know it.
TFM of FutureSoft
Also visit the CPC and Plus users favorite OS: FutureOS - The Revolution on CPC6128 and 6128Plus

Grim

On the Plus, the links to change the OEM (LK1/2/3) and frame-rate (LK4) are on the PCB near the ASIC. Wire LK2 and you have a Schneider Plus :)

Afaik, only the Spanish 464 ROM (s1) ignores the OEM links (and always shows Amstrad).

Powered by SMFPacks Menu Editor Mod