Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!rutgers!sunybcs!boulder!hao!oddjob!mimsy!umd5!hans From: hans@umd5.umd.edu (Hans Breitenlohner) Newsgroups: comp.sys.atari.8bit Subject: Re: (none) Message-ID: <1984@umd5.umd.edu> Date: Fri, 9-Oct-87 20:10:17 EDT Article-I.D.: umd5.1984 Posted: Fri Oct 9 20:10:17 1987 Date-Received: Mon, 12-Oct-87 00:47:13 EDT References: <8709230608.AA23983@ucbvax.Berkeley.EDU> Reply-To: hans@umd5 (Hans Breitenlohner) Organization: University of Maryland, College Park Lines: 56 In article <8709230608.AA23983@ucbvax.Berkeley.EDU> F1.GDM@ISUMVS.BITNET ("Gene Merritt") writes: >I just installed my new US Doublers and started using SpartaDos. Unfortunately >SpartaDos conflicts with my OmniView 256 chip. This disables a few functions >of SpartaDos that I would realy like to use. > >Is there any easy way to make a "ramrod xl" card that that will allow me to >choose between OmniView and the original OS? > >Can I make a board that sockets both chips and put a switch to the +5 lines to >activate the right chip at power up? >Do I need to worry about the ground wires? Can it be that simple? > >I would appreciate hearing from anyone that owns a Ramrod board, or has any >ideas. > >f1.gdm @ isumvs.bitnet This should be quite simple. I have never seen a ramrod or similar board, or tried this myself. Piggyback the two ROMs. All pins except 20 (chip enable) and 22 (output enable) can be connected directly. I will outline four possibilities for hooking up the select logic, each with its own set of advantages and dis- advantages. I would leave as much airspace as practical between the two ROMs. Note: This is based on information about 27128 EPROMs. While these schemes should work with ROMs, I do not know if they have the same poser-saving circuitry in them that the EPROMs have. 27128 EPROMs draw 100mA in active mode (CS/ low), 25mA in standby mode (CS/ high). The outputs are enabled only if CS/ and OE/ are both low. 1. Wire both pin 20s together, and connect to pin 20 on socket. Wire up a switch so that one pin 22 is grounded, the other pulled to +5V. Advantage: Only DC on switch. Disadvantage: Both ROMs will go from standby to active whenever the ROM is addressed. 2. same as one, but with pins 20 and 22 reversed. Advantage: Only DC on switch. Disadvantage: The switch-selected ROM will always be in active state 3. Pins 22 connected to each other and board. Wire up a switch so that the signal from pin 20 on the board is fed to pin 20 of one ROM, while pin 20 of the other is pulled to +5V. Advantage: Only the selected ROM is active, and only when needed. Disadvantage: Chip enable signal on switch and wiring, placement and construction are more critical. 4. By using suitable gates you can create the effect of solution 3, but without the drawback of having high-speed signals running to and through your switch. Disadvantage: More complex. Personally I would recommend solution 3, unless you want the switch outside the case, in which case I would recommend solution 2.