The following article by GŁnther (Bartl??) was previously published in ABBUC Magazine number 51.
Atleast since Hans-Christof Tuchen in magazin number 50 introduced his 'deluxe methode' of connecting a monochrome TTL monitor to the XEP80, it shouldn't be a problem anymore to find a suitable monitor for an excellent 80 character representation. But there seem to be people who categorically refuse to perform internal upgrades to their beloved Atari hardware. With some effort, this can be overcome. A small electronic circuit extracts the horizontal and vertical synchronisation signals from the composite video signal the XEP80 puts out on its RCA jack, and brings them to TTL level as needed for use with a TTL monitor. Both signals are available in two flavors, inverted and non-inverted. A variable resistor is used to take into account slight differences in video signal input and small amplifier is used to prevent quality loss. The required voltage of +5 Volt can be taken from one of the joystickports.
The quality of the signal is in no way worse if compared to the direct connection. The advantage being that one gets the possibility of not having to use a CVBS monitor without losing picture quality. The TTL monitor could be used as a video control monitor for instance, but it can just as well use the picture from the Atari that was made by ANTIC. Those of you who work under TurboDOS, will know, that this DOS does not support screen handling in XEP80 mode. But if you add a switch, one could feed the normal ANTIC picture to a TTL monitor. One could even put a small sound amplifier on the printed circuit board, since most TTL-monitors do not support sound.
Whether CVBS or TTL monitor, if you want to enjoy working/playing with or without the XEP80, a second monitor is needed. I've already heard from many people that they do not use the XEP80 simply because they do not have enough room for a second monitor, or because they do not want one because of 'cosmetic' reasons. So one would need a monitor that will support both modes to the fullest satisfaction of the user. Unfortunately, I have not found this 'super-monitor', but I did find on that comes very close. It's name: Philips CM8833.
The CM8833 is a CVBS monitor that can be recommended for everyday 40 column use with the XL/XE without hesitation. But because of the high resolution, it also delivers the best picture of all the monitors I know, when directly connected to the XEP80. This is enhanced by the ability to switch to a monochrome-green screen. But what makes this the ultimate monitor is that fact that it can handel both analog RGB (via the SCART connector) and RGB-TTL (via an 8 pin DIN connector). It automatically switches the vertical frequency between 50 and 60 Hz. Using analog RGB this monitor can for instance be used with both color modes of the Atari ST.
But on to connecting the XEP80 via RGB TTL:
Connecting it via above mentioned video TTL convertor is very easy. For the direct connection, the CM8833 only needs a vertical synchronisation signal, that is present at pin 8 of the 74LS86 (U6). The video signal is taken from R3 (the side that is connected to U4, pin 26), DIP switches can then be used to connect it to Red, Green, Blue and/or Intensity. The position of switches determines the color used on screen. It is also possible to take the intensity signal from U4 pin 25, as described by Hans-Christof Tuchen and then be switched via software.
The pin-out of the 8 pin DIN connector: pin 1: not connected pin 2: red pin 3: green pin 4: blue pin 5: intensity pin 6: ground pin 7: horizontal synchronisation pin 8: vertical synchronisationTo use monochrome monitors as well as the CM8833 directly, I have made the following connections to my test XEP80 (directly from the XEP80 to a SubD connector):
ground: (shield).................................pin 1 video : .........................................pin 7 vsync : U6 pin 8.................................pin 9 hsync : U6 pin 9....10kOhm variable resistor.....pin 8Inside the connector you'll not only find the 10kOhm variable resistor, but also a 4 pole DIP switch. With the help of this switch, it is possible to also connect the video signal - which is fixed to pin 7 - to pin 2 (red), pin 4 (green), pin 5 (blue) or pin 6 (intensity). Adaptor cables are used to connect the 9 pin connector (with pin out according to the standard) to the monitor in use. The variable resistor can be adjusted such that both monitors get a satifying signal.
The only thing missing is a connection from the RCA Audio connector to pin 2 (audio right) and pin 6 (audio left) of the SCART connector, so that the sound can be heard in both modes of operation. With the front mounted input switch it is easy to switch between both modes. Unfortunately, the 40 column switch is slightly smaller as that of the XEP80, but adjustments are made relatively easy (horizontal height is adjusted via a knob on the back). As I said, not perfect, but one can get used to this solution. By the way, the variable resistor for the horizontal frequency is on the main circuit board inside the CM8833 under the name R437.
Parts list: C1, C3, C4, C5, C7: Electrolytical capacitor 10uF/16V C2: Electrolytical capacitor 47uF/16V C6: 4700pF C8: 0.1uF R1: 100 Ohm R2, R16: 1k0 Ohm R3: 47k0 Ohm R4: 3k6 Ohm R5: 220 Ohm R6, R8, R10: 10k0 Ohm R7, R11, R12, R13: 470 Ohm R9: 3k0 Ohm R14: 100k Ohm R15: 18k0 Ohm R17: 82 Ohm R18: 200 Ohm P1: 100 Ohm P2: 4k7 Ohm D1: 1N4148 T1: BC414B T2: BC415B IC1: LM339 Connections: 5V : +5V stabilized (from joystick port) IN : video in (from XEP80) OUT : video out (video RGB) HOR : horizontal synchronisation TTL VER : vertical synchronisation TTL HOR and VER with a line on top: as above, but inverted The variable resistors: P1 adjust to incomming video signal (XEP80) P2 adjusts the level of amplification
[The Philips CM8833 might be known under an other name in the USA and Canada. Maybe even under the brand name 'Magnavox'. But Philips has also manufactored monitors for other companies. One of them is Commodore. I'm not sure about the 1700 and 1900 series, but the 1084 I own definitely is a Philips in disguise. The CM8833 supports stereo sound.
One way to get +5 Volts would be to not directly connect the XEP80 to a joystick port, but to connect it to a small circuit board. This circuit board would be connected to the joystickport. On the circuit board would be a connector where you could tap into the +5 Volt line. That way, you still have one joystick port left. If you know your way around electronics, you could even add an extra joystickport and use a switch to switch between XEP80 and the device connected to the second port on the circuit board.]