Re: [CAD_CAM_EDM_DRO] Motion control board

William Scalione wrote:

> Jon,
>
> Could you explain to me how the parallel port "tells" your step rate
> generator board to generate steps. Is it a "smart" board and you send
> it a command to move 10,000 steps at a certain acceleration and
> speed. If so could you expand on the commands required to do that.

No, that is too independent from the CPU. What my board does is
provide very tightly controlled VELOCITIES, and either counts encoder
pulses if the motors are so equipped, or it counts its own step pulses.
This info can be fed back to the CPU at high rates (1000 to 10,000 times
a second, generally). So, the computer sees an interface that looks
very much like a servo system. It tells the drive system how fast to
move, and gets position feedback.

In more detail, the IEEE-1284 specification defines a standard in which
the parallel port can address up to 256 different byte-wide registers.
For optimum performance, the peripheral can count up addresses, so you
can read from or write to a number of sequential addresses. Modern
PC parallel port hardware has a chip that allows the CPU to write or read a
byte to/from a register with a single instruction, with handshaking of the
data transfer. This mechanism can move over 1 million bytes/second,
which is plenty for controlling a multi-axis machine tool.

The reason for the encoder counters is that the step pulse generation
is totally independent from the CPU, other than specifying the rate. So,
the CPU has no idea WHEN a step pulse went out. This makes it hard
for the CPU to keep track of position without counting the pulses. To
relieve the CPU of this responsibility, counters are provided on the chip.
This allows step rates to 300,000 steps/second to be handled.

The step rate generator uses a 10 MHz clock, so it has a step rate
resolution
of 100 nS. With the 24-bit counter, step rates from .596 steps/sec to
5 million/sec are possible, depending on step pulse width. The width
of the step pulses can be programmed in 100 nS increments from
100 nS to 25.5 uS. Setup and hold delays on change of the direction
signal relative to the step pulses can also be set over the same range.
A DIP switch setting makes the direction line follow Gecko drive
conventions,
where the direction line can only change at the beginning of the step
pulses.

Other DIP switches select encoder feedback or open-loop (encoderless)
operation on an axis by axis basis. There is also a provision to generate
full-step phase waveforms like Bridgeport BOSS drivers use, again on an
axis by axis basis.

This module also has 16 digital inputs and positions on the board to mount
8 solid state relays.

Jon