The Craftmans Shop > New from Old
The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
Sea.dog:
I'm looking forwards to this thread hitting fifty pages :D
awemawson:
--- Quote from: Sea.dog on August 25, 2021, 03:20:28 PM ---I'm looking forwards to this thread hitting fifty pages :D
--- End quote ---
Just a short one then you think Graham :clap:
awemawson:
Well I've not been idle today, apart from taking grandson round Bodium Castle I've made progress on the circuit for the RAM card.
I've created a 'pin out' model for the actual RAM chips and the resistor arrays as they didn't exist in Protel, and I've started drawing an embryo circuit diagram with all the components, so that as I identify inter-connections I can edit the drawing accordingly. There is a 'dual analog precision comparator chip which did exist in Protel, and several SMD three legged (transistor / dual diode / MOSFET) SO-23 devices that are proving elusive to positively i/d. One is definitely a PNP transistor but hopefully the other three will become obvious as I map the circuit.
Rather fuzzy photos of them from several angles haven't really helped much - they are only 2.9 mm x 1.45 mm ! They have a very faint possibly 'A J' printed on them
I am expecting that the 'dual precision comparator' chip will be being used to monitor the back up battery level, as an alarm should be generated if it falls too low.
The unidentified three legged devices I'm pretty certain are in the change over circuit from normal to battery power - I'm attaching a circuit of a typical change over circuit that amusingly is servicing a similar static ram chip and this circuit will probably closely follow it.
Tomorrow if I get a chance I will model the 48 pin card connector and start doing the virtual wiring up - hopefully things then will become a bit clearer.
awemawson:
A bit of a hectic day today (grandson back to Hampshire, and two sets of cottage guests departing and arriving) but I did manage to draw up a skeleton pinout for the DIN41612 48 pin plug so I have places to anchor connections on the circuit diagram that I'm generating.
To that end I removed the mating socket from the original Interface Card that had been dissolved when the first RAM card spewed it's lithium juices before I got the machine. I reasoned that although interesting, I was never actually going to re-use it, so the manner of removing the 48 pin socket didn't have to be delicate.
. . . blowlamp to the rescue . . and off it came in excellent condition, which is more than can be said for the PCB it came off !
I can now start mapping the outside world contacts to the various address and data lines onboard the card.
Duty calls so more later.
awemawson:
Today I managed to trace out the address bus with it's associated pull up resistor packs, and the data bus, and get them on the circuit. The 15 address lines of the four RAM chips are commoned, the the data bits of two are commoned to form the least significant byte, and the other two are commoned to form the most significant byte of the 16 bit data word.
Although I've traced the logic for the chip select signals back to the card connector I've not yet sussed the switching between the two pairs of ram chips, this switching must form the 16th address bit to map all the memory.
Yet to do is trace out the Vcc (+5v) logic supply switching and the battery (3.7 volt) stand by switching that involves the various SMD chips and the analog comparator chip that I thinks is for low battery alarm.
It looks like some of the SMD chips may be power supervisory circuits:
"The PT7M7xxx family microprocessor (μP) supervisory
circuits are targeted to improve reliability and accuracy
of power-supply circuitry in μP systems. These devices
reduce the complexity and number of components
required to monitor power-supply and battery functions"
But that is more joy for tomorrow, I need to uncross my eyes !
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