The TEA VM gives each I/O (Input/Output) device a unique 2-byte address, or port ID.  System values, system constants, some reflex elements, and VM semaphores also have IO ports.  Additional features and operations may also be controlled with IO ports.  Each VM implementation will offer different subsets of these IO ports to allow the VM to interact with the specific I/O offered by the module or host where the VM is running.  Most of these ports duplicate the functionality of a command.

To write to an output device, push a value onto the stack.  Then pop that value into a device port with the popbm , popbmx , popsm , or popsmx command.  To read from an input device, push a value from a device port onto the stack using the pushmb , pushmbx , pushms , or pushmsx command.

The table below lists the ports and reserved address ranges for various I/O devices specific to the Moto 1.0 Module.  Some devices have multiple functions.  Each multi-function device gets a set of sequential port IDs.  The least significant bits of the port ID select the appropriate function.

The table also lists the ports along with the functions, access modes, and default data sizes associated with each port.  An asterisk (*) in the data size entry means that the size is strictly enforced.  Executing an opcode that uses a different data size will cause an error.  If there is no asterisk, the type will be converted appropriately.  A char will be padded with a zero byte to convert it to an int.  An int will be truncated to convert it to a char.

(See the GP Module IO Ports chart for a quick reference.)

Port Summary

aPortA2D

This group of memory addresses is reserved for A2D input access.  Each A2D device has two functions associated with it:

Reading an int from the A2D RD port pushes two bytes with the 10-bit analog conversion result onto the stack.  Reading a char from the A2D RD port pushes a byte with the 8 most significant bits of the conversion result onto the stack.

aPortDigital

This group of memory addresses is reserved for digital I/O pin access.  On the Moto module, each digital I/O pin has two functions associated with it:

Reading from the Digital CFG port pushes the current pin configuration onto the stack.  Writing to the Digital CFG port sets the pin configuration.  Reading from the Digital IO port pushes a 0 or 1 onto the stack depending on the pin state.  The pin must be configured as an input in order to read it.  Otherwise, a read will generate an error.  Writing to the Digital IO port sets the specified pin to 0 if the stack parameter is 0 or 1 if the stack parameter is non zero.  The pin must be configured as an output in order to write to it.  Otherwise, a write will generate an error.

aPortMoto

This group of memory addresses is reserved for access to motor control functions.  Each motor control channel has sixteen functions associated with it:

The CDUTY and CINPUT ports are read-only.  They are used to observe the current input and output of the PID control loop.

The RMPCFG port is write-only.  A control byte is written to the port to indicate a read or write of a ramp configuration parameter.  The high nibble must be 1 to indicate a read and 0 to indicate a write.  The low nibble is the index of the parameter to be accessed.  To perform a write, the 2-byte ramp control parameter must be on the stack prior to writing the control byte to the port.  After a read operation, the 2-byte ramp control parameter will be pushed onto the stack.

The RMPENA port is write-only.  A control byte is written to the port to select the desired enable/disable operation.  The high nibble must be 0 or 1 to indicate STOP or GO.  The low nibble is the index of the channel to enable/disable.  A low nibble of 0 or 1 indicates channel 0 or channel 1.  A low nibble of 2 applies the enable/disable operation to both channels.

All other ports are read/write capable and use a 2-byte parameter.

aPortMotoPIDErr

Writing any byte to this memory address will make the VM perform an operation that pushes four bytes onto the stack.  The first two bytes are an int with the signed error between the setpoint and feedback input for channel 0.  The last two bytes are an int with the signed error between the setpoint and feedback input for channel 1.  A user can access the Setpoint and CINPUT ports and do subtractions to get the same results, but using this port is more efficient.