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MC100E195FNG Fiches technique(PDF) 7 Page - ON Semiconductor |
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MC100E195FNG Fiches technique(HTML) 7 Page - ON Semiconductor |
7 / 11 page MC10E195, MC100E195 http://onsemi.com 7 VCCO ADDRESS BUS (A0−A6) A7 INPUT D1 D0 LEN VEE IN IN VBB VCC VCCO Q Q D1 D0 LEN VEE IN IN VBB VCC VCCO Q Q VCCO OUTPUT E195 Chip #1 E195 Chip #2 Figure 3. Cascading Interconnect Architecture Cascading Multiple E195’s To increase the programmable range of the E195 internal cascade circuitry has been included. This circuitry allows for the cascading of multiple E195’s without the need for any external gating. Furthermore this capability requires only one more address line per added E195. Obviously cascading multiple PDC’s will result in a larger programmable range however this increase is at the expense of a longer minimum delay. Figure 3 illustrates the interconnect scheme for cascading two E195’s. As can be seen, this scheme can easily be expanded for larger E195 chains. The D7 input of the E195 is the cascade control pin. With the interconnect scheme of Figure 3 when D7 is asserted it signals the need for a larger programmable range than is achievable with a single device. An expansion of the latch section of the block diagram is pictured below. Use of this diagram will simplify the explanation of how the cascade circuitry works. When D7 of chip #1 above is low the cascade output will also be low while the cascade bar output will be a logical high. In this condition the SET MIN pin of chip #2 will be asserted and thus all of the latches of chip #2 will be reset and the device will be set at its minimum delay. Since the RESET and SET inputs of the latches are overriding any changes on the A0−A6 address bus will not affect the operation of chip #2. Chip #1 on the other hand will have both SET MIN and SET MAX de-asserted so that its delay will be controlled entirely by the address bus A0−A6. If the delay needed is greater than can be achieved with 31.75 gate delays (1111111 on the A0−A6 address bus) D7 will be asserted to signal the need to cascade the delay to the next E195 device. When D7 is asserted the SET MIN pin of chip #2 will be de-asserted and the delay will be controlled by the A0−A6 address bus. Chip #1 on the other hand will have its SET MAX pin asserted resulting in the device delay to be independent of the A0−A6 address bus. When the SET MAX pin of chip #1 is asserted the D0 and D1 latches will be reset while the rest of the latches will be set. In addition, to maintain monotonicity an additional gate delay is selected in the cascade circuitry. As a result when D7 of chip #1 is asserted the delay increases from 31.75 gates to 32 gates. A 32 gate delay is the maximum delay setting for the E195. To expand this cascading scheme to more devices one simply needs to connect the D7 input and CASCADE outputs of the current most significant E195 to the new most significant E195 in the same manner as pictured in Figure 3. The only addition to the logic is the increase of one line to the address bus for cascade control of the second PDC. SET MIN SET MAX TO SELECT MULTIPLEXERS BIT 0 BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 D0 Q0 LEN Reset Reset D1 Q1 D2 Q2 D3 Q3 D4 Q4 D5 Q5 D6 Q6 D7 Q7 LEN LEN LEN LEN LEN LEN LEN CASCADE CASCADE Figure 4. Expansion of the Latch Section of the E195 Block Diagram Reset Reset Reset Reset Reset Reset Reset Reset Reset Reset Reset Reset Reset Reset |
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