Aucbvax.1783 fa.info-terms utzoo!duke!decvax!ucbvax!ATP.Tyson@UTEXAS-20 Tue Jun 16 22:07:07 1981 Meta key on Mime2a I have just gotten through modifying my Mime2a (board number M801213118) to have a Meta key. I thought I'd pass the info on about how to do it. The modification of my Mime2a to change the NUM key to a Meta key was rather simple but does require a minimal knowledge of electronics (which is all I have). Someone with no knowledge probably can do it but may have problems if they screw up. This patch has been done on Mime's from 2 different shipments but that doesn't guarantee it will be the same on your terminal. The Mime2a keyboard is connected by a flat cable of wires running from the keyboard to the PC board in the back of the terminal. When the NUM key is depressed, it grounds the wire to which it is connected. This in turn triggers the logic which does the conversion of the right hand keys to the numeric keypad. There is a switch on the back of the Mime2a that is labelled BIT 8. In one position, it forces the meta bit of the character sent to the computer to 0 (non-meta) while the other position forces the meta bit to 1 (meta). What is necessary to do is to disconnect the wire coming off the NUM key from the NUM circuitry. The signal off that wire must be inverted (switch from 0 volts to 5 volts and vice versa) and fed to the non-grounded side of the BIT 8 switch (which will be left in the open position). In order to do this, it will be necessary to use the open IC socket on the board. What I did was to go out to Radio Shack and get a 7404 IC to do the inverting and a little IC board (their part # 276-159). Since the 7404 has a different number of pins than the socket, it will be mounted on the IC board which will be mounted into the socket. To mount the IC board in the socket it is necessary to make some pins that fit into the IC socket. I had some old push-in terminals which I managed to cut and flatten so that they would fit into the IC socket. I used 4, one in each corner. You have to be careful in positioning them on the IC board when you solder them in so that they will still fit into the IC socket. A little thought should provide the best way to arrange this. I chose the solder pads so that when the 7404 was mounted onto the board, the ground (bottom right - All the directions I will give are as though the PC board was still in place and you are looking at it through the CRT) was directly connected to the solder pad holding the pin that goes to the ground (bottom right) in the socket. The upper left is the power input. I had to jumper from where the pin from the power supply for the socket (upper left) was connected to the board to where the IC would expect its power. A wire needs to be installed from one of the outputs of the inverters (say, pin 4) to the top side of the BIT 8 switch. Another wire will be needed to run from the input to that inverter (pin 3) down to where the flat cable from the keyboard is connected to the PC board. The connection of the wire at the keyboard cable end is the trickiest part. You need to have some pretty thin wire (at least 26 gauge) because it will need to go through a small hole in the PC board. Remove the keyboard cable from its socket and the other batch of wires that are connected to the PC board nearby. There are 3 solder pads near the upper left end of the keyboard cable socket. One of these (the middle one, closest to the socket) is connected to a small solder run that runs up the PC board and disappears under the IC just above the socket it. That is the one you want. On the backside of the PC board you will see that it is connected by a solder run to one of the pins (top row, sixth from the right as viewed from the back) on the socket and then to one of the pins of the IC below there. You may want to take an ohmeter and see that pressing the NUM key causes this circuit to be shorted to ground (while the terminal is off!). Now you should find where the other end of the solder run on the front (component) side of the PC board goes. It goes to the second pin (from the left as viewed from the component side) on the top side of the third of the big IC's below the IC socket we are going to use. Make sure you have the right pin by checking to see it is shorted to ground when the NUM key is pressed. Now you need to run a wire from this pin (actually, the corresponding socket pin) on the back (foil) side of the PC board to the pin (again, the socket pin) of the IC below the keyboard cable socket which we found above (connected by a solder runner to the pin of the socket to which the NUM key wire is connected). When this is done, break the solder runner between that pin and the keyboard cable socket. On the component (front) side of the PC board at that solder pad you found earlier, you should break the solder run that runs up the PC board. After doing this, you may want to make sure that the solder runs are indeed broken by checking that the solder pad is isolated from the pins of the IC sockets you soldered wires to. Now you can heat up the solder pad (on both sides of the board) and push the thin wire that comes down from the IC board you installed through the PC board. Try to be careful that you don't cause the solder pad on the back to be torn from the board. If you didn't do it before, solder in the IC and make sure the BIT 8 switch is open. At this point you may want to make sure that the terminal in local is not doing the NUM conversion for the right hand keys. If it is, you either didn't break the solder runs (if you get numbers with NUM depressed) or you don't have a correct connection on the jumper wire you installed on the back of the PC board. Then you ought to check to see that you are getting the Meta characters when you the NUM key depressed. Finally you will want to change the NUM key from a locking key to a normal type key. If you remove the top of the key by pulling it straight up, you will see a small pin on the top edge of the key. Work the key a few times to see how the mechanism works. By prying the pin towards the top of the keyboard, the rest of the key will pop out. Looking at the slot in which the pin goes in the piece that popped out you will see a raised heart shaped area. You need to carve this out so there is nothing for the pin to catch on. I used a little drill with a very small grinder on it to remove the plastic but I suppose any sharp instrument could be used. Now you have a Meta key on your Mime! Now, if anyone can tell me how to get rid of the bell on the character insert!? (By the way, padding with at least 8 CR's is faster than using all nulls because the damn thing looks to see if the buffer is almost empty. If so, it updates the screen in a very slow way.) ------- ----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen of http://communication.ucsd.edu/A-News/ This Usenet Oldnews Archive article may be copied and distributed freely, provided: 1. There is no money collected for the text(s) of the articles. 2. The following notice remains appended to each copy: The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.