PAL20X8 PAL DESIGN SPECIFICATION P7059 (PMSI402) BRAD MITCHELL 04/27/82 OCTAL DOWN COUNTER MMI FIELD APPLICATIONS ENGINEER DALLAS, TEXAS CLK I0 D0 D1 D2 D3 D4 D5 D6 D7 I1 GND /OC /BO Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q0 /BI VCC /Q0 := I1*/I0*/D0 ;LOAD D0 (LSB) + I1* I0* BI ;COUNT DOWN :+: I0*/Q0 ;COUNT DOWN/HOLD /Q1 := I1*/I0*/D1 ;LOAD D1 + I1* I0* BI*/Q0 ;COUNT DOWN :+: I0*/Q1 ;COUNT DOWN/HOLD /Q2 := I1*/I0*/D2 ;LOAD D2 + I1* I0* BI*/Q0*/Q1 ;COUNT DOWN :+: I0*/Q2 ;COUNT DOWN/HOLD /Q3 := I1*/I0*/D3 ;LOAD D3 + I1* I0* BI*/Q0*/Q1*/Q2 ;COUNT DOWN :+: I0*/Q3 ;COUNT DOWN/HOLD /Q4 := I1*/I0*/D4 ;LOAD D4 + I1* I0* BI*/Q0*/Q1*/Q2*/Q3 ;COUNT DOWN :+: I0*/Q4 ;COUNT DOWN/HOLD /Q5 := I1*/I0*/D5 ;LOAD D5 + I1* I0* BI*/Q0*/Q1*/Q2*/Q3*/Q4 ;COUNT DOWN :+: I0*/Q5 ;COUNT DOWN/HOLD /Q6 := I1*/I0*/D6 ;LOAD D6 + I1* I0* BI*/Q0*/Q1*/Q2*/Q3*/Q4*/Q5 ;COUNT DOWN :+: I0*/Q6 ;COUNT DOWN/HOLD /Q7 := I1*/I0*/D7 ;LOAD D7 (MSB) + I1* I0* BI*/Q0*/Q1*/Q2*/Q3*/Q4*/Q5*/Q6 ;COUNT DOWN :+: I0*/Q7 ;COUNT DOWN/HOLD IF (VCC) BO = BI*/Q0*/Q1*/Q2*/Q3*/Q4*/Q5*/Q6*/Q7 ;BORROW OUT FUNCTION TABLE CLK /OC I1 I0 D7 D6 D5 D4 D3 D2 D1 D0 /BI /BO Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q0 ; -INPUT-- -OUTPUT- ;CONTROL INSTR DDDDDDDD BORROW QQQQQQQQ COMMENTS ;CLK /OC I1 I0 76543210 /BI /BO 76543210 (HEX VALUES) ------------------------------------------------------------------------------- C L H L HHHHHHHL X H HHHHHHHL LOAD (FE) C L H H XXXXXXXX L H HHHHHHLH DECREMENT C L H L HHHHHHLL X H HHHHHHLL LOAD (FC) C L H H XXXXXXXX L H HHHHHLHH DECREMENT C L H L HHHHHLLL X H HHHHHLLL LOAD (F8) C L H H XXXXXXXX L H HHHHLHHH DECREMENT C L H L HHHHLLLL X H HHHHLLLL LOAD (F0) C L H H XXXXXXXX L H HHHLHHHH DECREMENT C L H L HHHLLLLL X H HHHLLLLL LOAD (E0) C L H H XXXXXXXX L H HHLHHHHH DECREMENT C L H L HHLLLLLL X H HHLLLLLL LOAD (C0) C L H H XXXXXXXX L H HLHHHHHH DECREMENT C L H L HLLLLLLL X H HLLLLLLL LOAD (80) C L H H XXXXXXXX L H LHHHHHHH DECREMENT C L H L LLLLLLLL L L LLLLLLLL LOAD (00) C L H H XXXXXXXX L H HHHHHHHH DECREMENT (ROLL UNDER) C L H L LLLLLLLL L L LLLLLLLL LOAD (00) C L H L LLLLLLLH X H LLLLLLLH LOAD (01) C L H L LLLLLLHL X H LLLLLLHL LOAD (02) C L H L LLLLLHLL X H LLLLLHLL LOAD (04) C L H L LLLLHLLL X H LLLLHLLL LOAD (08) C L H L LLLHLLLL X H LLLHLLLL LOAD (10) C L H L LLHLLLLL X H LLHLLLLL LOAD (20) C L H L LHLLLLLL X H LHLLLLLL LOAD (40) C L H L HLLLLLLL X H HLLLLLLL LOAD (80) C L H L LLLLLLLL L L LLLLLLLL LOAD (00) C L L L XXXXXXXX X H HHHHHHHH PRESET C L H H XXXXXXXX L H HHHHHHHL DECREMENT TO (FE) C L H H XXXXXXXX L H HHHHHHLH DECREMENT TO (FD) C L H H XXXXXXXX L H HHHHHHLL DECREMENT TO (FC) C L H H XXXXXXXX L H HHHHHLHH DECREMENT TO (FB) C L H H XXXXXXXX L H HHHHHLHL DECREMENT TO (FA) C L H H XXXXXXXX L H HHHHHLLH DECREMENT TO (F9) C L H H XXXXXXXX L H HHHHHLLL DECREMENT TO (F8) C L H H XXXXXXXX L H HHHHLHHH DECREMENT TO (F7) C L H H XXXXXXXX L H HHHHLHHL DECREMENT TO (F6) C L H H XXXXXXXX L H HHHHLHLH DECREMENT TO (F5) C L H H XXXXXXXX L H HHHHLHLL DECREMENT TO (F4) C L H H XXXXXXXX L H HHHHLLHH DECREMENT TO (F3) C L H H XXXXXXXX L H HHHHLLHL DECREMENT TO (F2) C L H H XXXXXXXX L H HHHHLLLH DECREMENT TO (F1) C L H H XXXXXXXX L H HHHHLLLL DECREMENT TO (F0) C L H L LLLLLLLH X H LLLLLLLH LOAD (01) C L H H XXXXXXXX L L LLLLLLLL DECREMENT TO (00) /BO=L C L H H XXXXXXXX H H LLLLLLLL BI INHIBITS COUNT AND BO C L L H HHHHHHHH L L LLLLLLLL HOLD SEL INHIBITS COUNT ONLY C L H H LLLLLLLL L H HHHHHHHH DECREMENT TO (FF) X H X X XXXXXXXX X X ZZZZZZZZ TEST HI-Z ------------------------------------------------------------------------------- DESCRIPTION THIS IS AN 8-BIT SYNCHRONOUS DOWN COUNTER WITH PARALLEL LOAD, PRESET, AND HOLD CAPABILITY. THE LOAD OPERATION LOADS THE INPUTS (D7-D0) INTO THE OUTPUT REGISTER (Q7-Q0). THE PRESET OPERATION SETS THE OUTPUT REGISTER TO ALL HIGHS. THE HOLD OPERATION HOLDS THE PREVIOUS VALUE REGARDLESS OF CLOCK TRANSITIONS. THE DECREMENT OPERATION SUBTRACTS ONE FROM THE OUTPUT REGISTER WHEN THE BORROW- IN IS TRUE (/BI=L), OTHERWISE THE OPERATION IS A HOLD. THE BORROW-OUT (/BO) IS TRUE (/BO=L) WHEN THE OUTPUT REGISTER (Q7-Q0) IS ALL LOWS, OTHERWISE FALSE (/BO=H). THESE OPERATIONS ARE EXERCISED IN THE FUNCTION TABLE AND SUMMARIZED IN THE OPERATIONS TABLE: /OC CLK I1 I0 /BI D7-D0 Q7-Q0 OPERATION --------------------------------------------------- H X X X X X Z HI-Z L C L L X X H PRESET L C L H X X Q HOLD L C H L X D D LOAD L C H H H X Q HOLD L C H H L X Q MINUS 1 DECREMENT --------------------------------------------------- TWO OR MORE OCTAL DOWN COUNTERS MAY BE CASCADED TO PROVIDE LARGER COUNTERS. THE OPERATION CODES WERE CHOSEN SUCH THAT WHEN I1 IS HIGH, I0 MAY BE USED TO SELECT BETWEEN LOAD AND DECREMENT AS IN A BUS ADDRESSER (JUMP/DECREMENT). ALSO BORROW-OUT (/BO) AND BORROW-IN (/BI) ARE LOCATED ON PINS 14 AND 23 RESPECTIVELY WHICH PROVIDES FOR CONVENIENT INTERCONNECTIONS WHEN TWO OR MORE OCTAL DOWN COUNTERS ARE CASCADED TO IMPLEMENT LARGER DOWN COUNTERS.