. LSI Logic - Index of

SN54AS1B1A, SN54ASBB1A, SN74AS1B1A, SN74ASBB1AARITHMETIC lOGIC UNITS/FUNCTION GENERATORSdescription (continued)The' AS881 A has the same pinout and same functionality as the' AS 181 A except for the P, (3, and Cn + 4outputs when the device is in the logic mode (M = H).In the logic mode the' AS881 A provides the user with a status check on the input words A and 8, andthe ouput word F. While in the logic mode the fl, (3, and Cn + 4 outputs supply status information basedupon the following logical combinations:P=FO+F1 +F2+F3G=HC n +4=PCnFUNCTION TABLE FOR INPUT BITS EQUAL/NOT EQUALSO-S3-H. SI-S2-L. and M-HFUNCTION TABLE FOR INPUT PAIRS HIGH/NOT HIGHSO-SI-S3-L. S2-H • .and M-Hc nHLXXXXOUTPUTSOUTPUTSDATA INPUTSC nDATA INPUTSG P Cn +4G P Cn +4AO=BO Al =Bl A2=B2 A3=B3 H L H AO or BO = L Al or Bl = L A2 or B2 = L A3 or B3 = L H L HAO=80 Al =81 A2=82 A3=83 H L L AO or BO = L AlorBl = L A2 or B2 = L A3 or 83 = L H LAO*80 X X H H X AO=BO=H X X X H HX Al *81 X X H H X X Al=Bl=H X X H HX A2*B2 X H H X X X A2=82 =H X H HX X A3*B3 H H X X X A3=B3=H H HThe combination of signals on the S3 through SO control lines determine the operation performed on thedata words to generate the output" bits Fi. 8y monitoring the P and Cn + 4 outputs, the user can determineif all pairs of input bits are equal (see table above) or if any pair of inputs are both high (see table above).The' AS881 A has the unique feature of providing an A = 8 status while the exclusive-OR( e) functionis being utilized. When the control inputs (S3, S2, S1, SO) equal H, L, L, H; a status check isgenerated to determine whether all pairs (Ai, Bi) are equal in the following manner:P = (AO e 80) + (A 1 e 81) + (A2 e 82) + (A3 e 83). This unique bit-by-bit comparison of the datawords, which is available on the totem-pole P output, is particularly useful when cascading' AS881 s. Asthe A = 8 condition is sensed in the first stage, the signal is propagated through the same ports usedfor carry generation in the arithmetic mode (P and G). Thus the A = 8 status is transmitted to the secondstage more quickly without the need for external multiplexing logic. The A = 8 open-collector output allowsthe user to check the validity of the bit-by-bit result by comparing the two signals for parity.If the user wishes to check for any pair of data inputs (Ai, Bi) being high, it is necessary to set the controllines (S3,S2,S1 ,SO) to L, H, L, L. The data pairs will then be ANDed together and the results ORed inthe following manner: P = AOBO+A"B1 +A2B2+A3B3.signal designations53 I 52 I 51 I 50 I M I P = FO+F1 +F2+F3L 1 H I L I L I H I A080+A1B1 +A2B2+A383H I L I L I H L H I (AO EB 80)+(A1 EB 81)+(A2 EB 82)+(A3 ED 83)In both Figures 1 and 2, the polarity indicators (I::::::.. ) indicate that the associated input or output is activelowwith respect to the function shown inside the symbol and the symbols are the same in both figures.The signal designations in Figure 1 agree with the indicated internal functions based on active-low data,and are for use with the logic functions and arithmetic operations shown in Table 1. The signal designationshave been changed in Figure 2 to accommodate the logic functions and arithmetic operations for the activehighdata given in Table 2. The 'AS181A and 'AS881A together with 'AS882 and 'S182 can be usedwith the signal designation of either Figure 1 or Figure 2.TEXAS ~, INSTRUMENTSPOST OFFICE BOX 225012 • DALLAS. TEXAS 752652-5