()()()()()()()()¢¢ A 130XE-COMPATIBLE 256K ¢UPGRADE FOR THE ATARI 800XL¢ ¢by Claus Buchholz¢¢ I designed the 256K upgrade ¢described in my article, "The Quarter-Meg¢ Atari" (BYTE, September, 1985), in ¢December, 1984. Since this predated the¢ 130XE, there was no precedent for ¢extended memory on the XLs. I felt ¢free to implement a system of eight 32K¢banks. The major reason was to keep the¢ add-on circuit as simple as possible.¢ The 130XE, introduced in early ¢1985, set a different standard for¢ bank-select memory. It uses 16K ¢banks and makes them separately ¢available to both the CPU and the video¢controller (ANTIC). The XE has 128K ¢total memory. The 64K extended RAM is¢split into four 16K banks.¢ A 256K 800XL has 192K extended ¢RAM, which requires 12 16K banks. I¢have designed a new upgrade for the¢800XL that implements such a scheme.¢Its similarity to the 130XE's scheme ¢allows use of software for the XE on ¢a 256K 800XL.¢ To select one of four banks, ¢the XE uses two bits, #2 and #3, in the¢ memory control register (port B of ¢the 6520 PIA, addressed at $D301 or ¢54017 decimal). Zeroing bit #4 makes¢the selected bank appear at addresses¢ $4000-$7FFF (16384 to 32767 ¢decimal), as seen by the CPU. Zeroing ¢bit #5 makes it appear there as seen by¢ANTIC.¢ In my upgrade, bits #2, #3, #5 ¢and #6 select one of the twelve banks.¢ Zeroing bit #4 makes the selected ¢bank appear at $4000-$7FFF to both the¢CPU and ANTIC. So, any program for the ¢XE that uses the extended RAM for CPU¢ storage will work on an 800XL with ¢this mod. Those programs won't use the¢ additional 128K, though. Programs ¢that use the video banking feature of ¢the XE might run on the modified XL,¢but the screen display will be wrong.¢ The procedure for this upgrade ¢is basically the same as in the¢article, except for the following¢points. If your ANTIC (U7) part number¢is CO21697, use the circuit described¢by the first connection list below. If¢it is CO12296, include the circuit in¢the second list. The circuit requires ¢five connections to the PIA (U23). So, ¢pins 12 through 16 must be bent up ¢and connected to the circuit. The rest ¢of the procedure is the same. Notice ¢that this circuit has one more chip¢than the article's circuit. This is the¢price of compatibility.¢ With the 256K dynamic RAMs in ¢your XL, be sure to wait at least ten¢ seconds after turning the computer ¢off. Otherwise it may not coldstart¢ properly when you turn it back on.¢ My original RAMdisk software ¢doesn't work with this new mod, so I ¢have written a new version. It is used in the same way, except that it offers a choice of either two single-density ¢RAMdisks or one double-density. If ¢you wish a disk copy of the source and ¢object code, send me a blank disk and¢ return mailer with full postage, and ¢I will promptly send it back with the¢ software. Alternately, you may ¢download the software from the ¢Capitol Hill¢ Atari Owners' Society BBS at ¢517-371-1106 or from the Castle ¢Communications board at 517-371-4234.¢The source file is called QMEGXLD.SRC for Quater-MEG XL Double.¢ Also available is a RAMdisk ¢program that sets up one single-density¢ RAMdisk and leaves the XE-equivalent ¢banks free for XE software. This is¢ quite useful with BASIC XE, DOS 2.5, ¢or the new Synapse software. Its name¢ is QMEGXLS.SRC.¢ I ask one thing in return for ¢this information: Please pass it ¢around to all your interested friends.¢Put it in your club's library or on¢your favorite BBS. Encouraging software¢¢support of 256K will result in many¢ interesting uses for it. Thank you ¢and enjoy!¢¢ DEFINITION OF MEMORY CONTROL ¢REGISTER AT $D301 (54017 DECIMAL)¢¢ XL MOD 130XE¢¢ bit: 7 6 5 4 3 2 1 0 bit: 7 ¢6 5 4 3 2 1 0¢ D a b E c d B R D V C ¢x y B R¢¢ D=0 enables diagnostic ROM D=0 ¢enables diagnostic ROM¢ B=0 enables BASIC ROM B=0 enables ¢BASIC ROM¢ R=1 enables OS ROM R=1 enables OS ¢ROM¢ E=0 enables extended RAM V=0 ¢enables extended RAM for video¢ abcd is 4-bit extended RAM bank # ¢C=0 enables extended RAM for CPU¢ - ranges from 4 to 15 xy is ¢2-bit extended RAM bank #¢ - banks 12 to 15 are ¢equivalent - ranges from 0 to 3¢ to XE's banks 0 to 3¢¢ ¢PARTS LIST¢¢ 8 41256 256K-bit dynamic RAM ¢(200ns or less)¢ 1 74LS153 Dual 4-to-1 ¢multiplexer (IC2)¢ 1 74LS139 Dual 2-to-4 decoder ¢(IC3)¢ 1 - 33 ohm, 1/4 watt resistor¢¢ ADDITIONAL ¢PARTS FOR ANTIC #CO12296¢¢ 1 74LS158 Quad inverting 2-to-1 ¢multiplexer (IC4)¢ 1 74LS393 Dual 4-bit counter ¢(IC5)¢¢ LIST OF CONNECTIONS ¢FOR THE UPGRADE CIRCUIT¢¢ Instead of a drawing of the ¢upgrade circuit, below is a list of¢ connections. Each entry in the list ¢begins with the name of the signal¢ followed by all the IC pins that ¢connect together and share the ¢signal.¢ IC3-13 means pin 13 of IC3. The IC ¢numbers appear in the parts list ¢above.¢ IC1 is the 74LS158 chip from socket ¢U27 on the XL motherboard. DIP is the¢ DIP header to be plugged into socket ¢U27. U23-xx refers to the pins you ¢bend¢ up on the PIA chip at U23 on the ¢motherboard.¢¢ Vcc : DIP-16, IC1-16, IC2-16, ¢IC3-16, IC3-13¢ Vss : DIP-8, IC1-8, IC2-8, ¢IC2-1, IC2-15, IC3-8¢ A7 : DIP-11, IC2-10, IC2-11¢ A15 : DIP-10, IC2-13, IC3-3¢ A6 : DIP-14, IC2-6, IC2-5¢ A14 : DIP-13, IC2-3, IC3-2¢ MUX : DIP-1, IC1-1, IC2-2¢ A4 : DIP-2, IC1-2¢ A12 : DIP-3, IC1-3¢ RA4 : IC1-4, DIP-4¢ A5 : DIP-5, IC1-5¢¢ A13 : DIP-6, IC1-6¢ RA5 : IC1-7, DIP-7¢ -E : DIP-15, IC1-15¢ RA7 : IC2-9, DIP-9¢ RA6 : IC2-7, DIP-12¢ PB2 : U23-12, IC2-4¢ PB3 : U23-13, IC2-12¢ PB4 : U23-14, IC3-1¢ PB5 : U23-15, IC1-10¢ PB6 : U23-16, IC1-11¢ -Zd : IC1-9, IC3-14¢ -O1a : IC3-5, IC3-15, IC2-14¢ -O2b : IC3-10, One side of ¢resistor¢ RA8 : Other side of resistor, ¢Pin 1 of all RAMs¢¢ If your U7 part number is ¢CO12296, do not connect signal A7 ¢above, and¢ make the following additional ¢connections. The connection to U7 is ¢to a¢ trace on the motherboard that runs ¢from pin 8 of U7.¢¢ Vcc : DIP-16, IC4-16, IC5-14, ¢IC4-3¢ Vss : DIP-8, IC4-8, IC4-2, ¢IC4-15, IC5-7, IC5-2, IC5-12¢ A7 : DIP-11, IC4-6¢ -REF : U7-8, IC4-1¢ REF : IC4-4, IC5-1¢ A7' : IC4-7, IC2-10, IC2-11¢ Q7 : IC5-8, IC4-5¢ Q3 : IC5-6, IC5-13¢¢JJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJ¢JJJJJJJJJJJJJJJ
