MC100E016 Просмотр технического описания (PDF) - Motorola => Freescale

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MC100E016

8-Bit Synchronous Binary Up Counter

Motorola => Freescale 

MC10E016 MC100E016

Applications Information (continued)

EL01

Q0 –> Q7

LO CE

PE

E016

LSB

CLK TC

CLOCK

PO –> P7

Q0 –> Q7

CE

PE

E016

Q0 –> Q7

CE

PE

E016

CLK TC

EL01

PO –> P7

CLK TC

EL01

PO –> P7

Figure 4. 32-Bit Cascaded E016 Programmable Divider

Q0 –> Q7

CE

PE

E016

MSB

CLK TC

PO –> P7

Figure 4 on the following page shows a typical block

diagram of a 32-bit divider chain. Once again to maximize the

frequency of operation EL01 OR gates were used. For lower

frequency applications a slower OR gate could replace the

EL01. Note that for a 16-bit divider the OR function feeding the

PE (program enable) input CANNOT be replaced by a wire OR

tie as the TC output of the least significant E016 must also feed

the CE input of the most significant E016. If the two TC outputs

were OR tied the cascaded count operation would not operate

properly. Because in the cascaded form the PE feedback is

external and requires external gating, the maximum frequency

of operation will be significantly less than the same operation

in a single device.

Maximizing E016 Count Frequency

The E016 device produces 9 fast transitioning single ended

outputs, thus VCC noise can become significant in situations

where all of the outputs switch simultaneously in the same

direction. This VCC noise can negatively impact the maximum

frequency of operation of the device. Since the device does

not need to have the Q outputs terminated to count properly,

it is recommended that if the outputs are not going to be used

in the rest of the system they should be left unterminated. In

addition, if only a subset of the Q outputs are used in the

system only those outputs should be terminated. Not

terminating the unused outputs will not only cut down the VCC

noise generated but will also save in total system power

dissipation. Following these guidelines will allow designers to

either be more aggressive in their designs or provide them

with an extra margin to the published data book specifications.

MOTOROLA

2–6

ECLinPS and ECLinPS Lite

DL140 — Rev 4

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