The AMD 9513 Counter/Timer

Our CyCTM-series boards are based on the AMD 9513 System Timing Controller chip. Since the features described for these boards are virtually identical to the hardware features of the AMD 9513, I’ll focus on the software issues. The AMD 9513 is addressed as two locations: a control port and a data port. The control port provides direct access to the Status and Command registers, as well as allowing the user to update the data point register. The data port is used to communicate with all other addressable internal locations.

Each of the 5 general-purpose counters is independently controlled by its Counter Mode register. Through this register, a user can software select one of 16 sources as the counter input, a variety of gating and repetition modes, up or down counting in binary or BCD, and active-high or active-low input and output polarities. A Master Mode register controls the options which do not pertain to one of the 5 specific counters.

Any one of 24 different preset operating modes may be easily selected. These include software and hardware-triggered strobes or one-shot pulses. You set the counter to run in “Mode A” thru “Mode X” simply by setting 3 bits in the Counter Mode register.

A Load Register and a Hold Register are associated with each counter. The Load register is used to automatically reload the counter to any pre-defined value, thus controlling the effective count period. The Hold Register can be used to save intermediate counts without disturbing the count process, or to generate complex output waveforms when it is used as a second Load Register.

A powerful command structure simplifies user interaction with the counters. ARM and DISARM commands permit software gating of the count process. The LOAD command causes the counter to be reloaded with the value stored in either the Load register or the Hold register. It may be used as a software retrigger or for counter initialization. A SAVE command transfers the contents of a counter to its Hold register. The DISARM command disables further counting. The STEP command increments or decrements the counter. Additional commands are provided to set and clear an output toggle, issue a reset, and to clear and set special bits. Detailed information is provided with each CyCTM card.

Counters work best when the inputs have sharp, clean edges. Often the signal source is a button or switch that bounces or glitches, or the signal might be 0~24V or a voltage higher than TTL levels. The answer: voltage dividers and low-pass filter circuits are included on our STA 01 Universal Screw Terminal Panel. To de-bounce a counter input, simply populate one of the low-pass filter circuits and connect it to the counter’s input signal.