MC100E136

Overview
The MC10E/100E136 is a 6-bit synchronous, presettable, cascadable universal counter. Using the S1 and S2 control
pins the user can select between preset, count up, count down and hold count. The master reset pin will reset the
internal counter, and set the COUT, COUT, and CLIN, flip-flops. Unlike previous 136 type counters the carry out
outputs will go to a high state during the preset operation. In addition since the carry out outputs are registered they will not go low if terminal count is loaded into the register. The look-ahead-carry out output functions similarly.

Note from the schematic the use of the master information from the least significant bits for control of the two carry out functions. This architecture not only reduces the carry out delay, but is essential to incorporate the registered carry out functions. In addition to being faster, because these functions are registered the resulting carry out signals are stable and glitch free.

Cascading Multiple E136 Devices
Many applications require counters significantly larger than the 6 bits available with the E136. For these applications several E136 devices can be cascaded to increase the bit width of the counter to meet the needs of the application.

In the past cascading several 136 type universal counters necessarily impacted the maximum count frequency of the resulting counter chain. This performance impact was the result of the terminal count signal of the lower order counters having to ripple through the entire counter chain. As a result past counters of this type were not widely used in large bit counter applications.

An alternative counter architecture similar to the E016 binary counter was implemented to alleviate the need to ripple propagate the terminal count signal. Unfortunately these types of counters require external gating for cascading
designs of more than two devices. In addition to requiring additional components, these external gates limit the
cascaded count frequency to a value less than the free running count frequency of a single counter. Although there is
a performance impact with this type of architecture it is minor compared to the impact of the ripple propagate designs. As a result the E016 type counters have been used extensively in applications requiring very high speed, wide bit width synchronous counters.

Motorola has incorporated several improvements to past universal counter designs in the E136 universal counter.
These enhancements make the E136 the unparalleled leader in its class. With the addition of look-ahead-carry features on the terminal count signal, very large counter chains can be designed which function at very nearly the same clock frequency as a single free running device. More importantly these counter chains require no external gating. Figure 1 below illustrates the interconnect scheme for using the look-ahead-carry features of the E136 counter.