Dynamic Shift Registers - Bitsavers - Trailing-Edge

U)EQ)...U)>til..."0coo.c>Q)~c- ...Q)Q)()CO...cTABLE 2. American Standard Code for Information Interchangeb 7 a a a a 1 1 1 1bs a a 1 1 a a 1 1____.bs a 1 a 1 a 1 a 1Bit b4 b 3 b 2 b,~ a 1 2 3 4 5 6 7Ia a a a a NUL OLE SP a @ P pa a a 1 1 SOH DCl ! 1 A G a qa a 1 a 2 STX DC2 " 2 B R b ra a 1 1 3 ETX DC3 # 3 C S c sa 1 a a 4 EOT DC4 $ 4 0 T d ta 1 a 1 5 ENG NAK % 5 E U e ua 1 1 a 6 ACK SYN & 6 F V f va 1 1 1 7 BEL ETB 7 G W g w1 a a a 8 BS CAN ( 8 H X h x1 a a 1 9 HT EM ) 9 I Y i Y1 a 1 a 10 LF SUB * : J Z j z1 a 1 1 11 VT ESC + K [ k I1 1 0 a 12 FF FS < L \ I1 1 a 1 13 CR GS - - M J m !~1 1 1 a 14 SO RS > N~ n1 1 1 1 15 SI US / ? 0 - 0 DEL~ I j I jROW -This coded character set is to be used for the general interchange of information among information processing systems,communication systems, and associated equipment.NInIZ«trol codes are identical with the numerics sectionof this device, except that bit b6 is a logic "0"instead of "1 n. The lower case letters are the sameas the capital letters (alpha section) except thatbit b6 is a logic "1" instead of "0". A glance atthe 7-bit ASCII standard MAPS (Table 2) willshow this to be consistent with the acceptedstandard. The manner in which this is implementedin our stand alone system is as follows: When thecontrol key is depressed bit b6 is slaved low in theoutput of the serial to parallel shift register, then ifthe numeric characters are being generated by theKI, control codes will result in the output of theshift register. If character key $, for example, wasdepressed, the resulting data code from the serialto parallel converter would be modified from01001000 ($) to 00001000 (EDT).The features of the KI chip will permit a moreelaborate system than this, but this is all that isrequired to accomplish the use of the KI chip intoa bipolar system. The total parts count is asfollows:1 - MM57041 - DM88502 - SN741071 - MH00251 - DM88002 - DM85704 - DM74001 - SN7404PROGRAMMING THE KEYBOARDINTERFACE CHIPWithin this device, there are nine areas that may bespecified, or programmed, by the customer. Thelargest of these is the encoding ROM with its 649-bit words. The ROM is actually programmedduring the process with a masking step that eitherleaves or removes gate oxide from a given nodedepending upon whether a 1 or 0 is desired fromthat node. To assist in programming the modulusof D and E counters, which may vary from 1 to15, vital information pertaining to keyboard performanceis required. This information will enablethe KI chip to overcome T line delays and switchbounce as explained in an earlier section of thisarticle. The D counter clock may also be specifiedto be either 8 in or CM. The fifth area to be specifiedas the static switch recognition code. If morethan one chip is used in any given system, eachchip must be given a unique internal code that willenable it to respond when the system calls forstatic switch data from a specific device.The sixth area to be defined is an option that willpermit the static switch information to be generatedfrom normally open, or normally closed,switch contacts. The seventh programmable functionpermits specifying the shift key switch aseither normally open or closed. Within the chipitself, these functions are implemented by inserting,or not inserting an inverter in the appropriateplace. Programmable function number eight per-260