CY545

Chapter 18
Electrical Specifications

CY545B Electrical Specifications

Absolute Maximum Ratings

  Ambient Temperature under bias .............. 0C to +70C
  Storage Temperature ......................... -65C to +150C
  Voltage on any pin with respect to ground ... -0.5V to Vcc+0.5V
  Power dissipation ........................... 1.0 Watts

DC & Operating Characteristics
(TA = 0C to +70C, Vcc = +5V +/-10%)

Electrical Conventions

All CY545 signals are based on a positive logic convention, with a high voltage representing a "1" and a low voltage representing a "0". Signals which are active low are indicated by a bar over or slash after the pin name, i.e., BUSY/.

All input lines except the data bus include weak pull-up resistors. If the pins are left open, the input signals will be high. The data bus pins must have external pull-up resistors to output a high value. Where appropriate, an input line will be considered in the floating state if the CY545 can drive it both high and low.

The data bus is bidirectional, and is tri-state during nonactive modes. Note that data bus signals are positive logic.

Reset Circuitry

The Restart line (pin#9) must be held high upon power-up to properly initialize the CY545. This may be accomplished by using a 4.7 uFd capacitor, as shown in Figure 18.1. Restart must be high for 10 milliseconds after power stabilizes on power-up. Once the CY545 is running, Restart need only be high for about 10 microseconds (11 MHz crystal).

Clock Circuits

The CY545 may be operated with crystal or external clock circuits. These two options are shown in Figure 18.2. All timing discussed in this manual assumes an 11.059 MHz series resonant crystal. Note that 11.0 MHz, such as a CTS Knights MP110 or equivalent will work fine. The CY545 requires an 11 MHz clock in order to generate the standard baud rates, although any crystal in the allowable range can be used with the adaptive mode, within the timing resolution limits of the CY545. Use 7.3728 MHz to make the fastest possible rate a standard 38400 baud, or 14.7456 MHz for 76,800 baud.