2 - Forth Interest Group

: >ON ( b --1 #PORT bset , \ turn ON device
: >OFF ( b --1 #PORT breset ; \ turn OFF device
: TOGGLE ( b -- ) #PORT btoggle ; \ TOGGLE device
: KILL ( -- ) 00 #PORT pc ! ; \ turn OFF all devices
: ALL-ON ( -- ) $FF #PORT pc! ; \ turn ON all devices
: ON? ( b - - f ) #PORT pc@ and O ; \ get ON status of device
: OFF? ( b - - f ) #PORT pc@ and 0= ; \ get OFF status of device
: WRITE (b--) #PORT pc! ; \ WRITE byte to port
: READ (--b) #PORT pc@ . ; \ READ byte at port
: BINARY ( -- ) 2 base ! \ change base to binary
: TOGGLE ( b --- ) #PORT BTOGGLE ;
The word TOGGLE can be used to change the status of any
device on the port. If the device is on, a TOGGLE command
will turn it off. If the device is off, a TOGGLE command will
turn it on. This command can be useful to create digital
pulses. It will take the present condition of port bit and
invert it for a selected time, then toggle it again to the
original condition.
FAN TOGGLE
If fan is on, the command will turn it off.
If fan is off, the command will turn it on.
The words ALL-ON and KILL will control the states of
all devices:
: KILL ( --- ) 00 #PORT PC! ;
: ALL-ON ( --- 1 $FF #PORT PC! ;
The word KILL can be used to shut down all devices
on the port. It can also be used at the beginning of the
program to clear the port to a known condition.
ALL-ON
will turn on all devices
KILL
will turn off all devices.
We can now make some words that will check the
status of each device. After a status check of a device, a
branch can occur depending on the flag value.
: ON? ( b --- f ) #PORT PC@ AND O ;
: OFF? ( b --- f ) #PORT PC@ AND O= ;
FAN ON?
Will return a true flag if the device is on, or a false flag if
it is off.
July 1995 August
FAN OFF?
Will return a true flag if the device is off, or a false flag if
it is on.
To turn on or off any combination of devices, we can
use the following code:
: BINARY ( --- ) 2 BASE ! ;
BINARY
11110000 WRITE
The output port will match the binary byte. A "1" will cause
the LED to be on. A "0" will cause the LED to be off.
READ
will show the status of the port (e.g., 11 110000).
Note: Any error will cause BASE to go back to DECIMAL.
Here are some other commands we can try. On the
same line, type:
MOTOR TOGGLE 2 SECONDS MANY
The MOTOR LED will blink on and off every two seconds.
To end the cycle, hit any key.
MOTOR >ON 2 SECONDS MOTOR >OFF
2 SECONDS 10 TIMES
The MOTOR LED will come on for two seconds and then
off for two seconds. This will be repeated ten times.
To speed it up, type:
MOTOR >ON 10 0 MS MOTOR >OFF
100 MS 10 TIMES.
The on/off time has been changed to 100 milliseconds.
To build more complex control structures, we can
incorporate multiple devices in the control byte. In our
imaginary factory, we have a large mixing tank that needs
to be cleaned out at the end of the day. To do this, we open
up the VALVE at the bottom of the tank and PUMP water into
it. After the tank is flushed out, we turn off the PUMP and
22 Forth Dimensions