Silicon Laboratories Stepper Machine Manual de usuario descargar pdf (Pagina 12)

AN155

12 Rev. 1.1

and set the doneFlag. The doneFlag is used as a

handshaking mechanism for the main loop to display

the done message.

If the motor state is not Done, the timer ISR will

calculate the value for the next interrupt and write to the

TL0 and TH0 special function registers. Next the

TableIndex or SlewCount is modified according to

the motor State. During Acceleration, the TableIndex

is incremented. During Deceleration the TableIndex is

decremented. If the motor state is Slewing the

SlewCount will be decremented.

5.5. UART Functions

The UART functions implement fully buffered I/O using

the C8051 receiver and transmitter. The benefit of using

buffered I/O is that most short messages will be sent or

received in a non-blocking manner. This means that the

CPU does not have to wait for each byte to be

transmitter or received. The user code does not write or

read data directly to the serial port. Instead the user

functions write or read data to the buffers. A UART

interrupt service routine transmits characters from the

write buffer and places received characters into the read

buffer.

The UART functions are modeled after the ANSI stdio

library functions. Each function has been optimized for

use in a small microcontroller. This is more code

efficient than including the entire stdio library and

rewriting the bottom layer functions.

The put string puts() function is used to display

messages on the terminal. There are two versions of

the get integer & put integer functions, one for 8-bit

unsigned char data and one for 16-bit unsigned int data.

The middle layers of the serial protocol are the put

character putc() and get character getc() functions.

These are the lowest level functions that should be

called by the user code.

The bottom layers of the serial communications protocol

are the write character writec() and read character

readc() functions. These functions write and read

directly to the read and write buffers. These functions

are called from the getc() and putc() functions. The

user code should not use readc() and writec()

functions directly. The readc() and writec()

functions momentarily disable UART interrupts while

accessing the read and write buffers to avoid

contentions. The writec() function also restarts the

transmitter if it is idle.

A single UART Interrupt service routine UART_ISR is

used for both transmit and receive interrupts. The ISR

must check both the transmitter and receiver to

determine which needs servicing. If the write buffer is

empty, the UART_ISR will set the TX_Idle flag bit and

clear the transmit interrupt flag without writing to SBUF0.

This will disable the transmitter until restarted. The

TX_Idle flag bit is used for handshaking with the

writec() function. The writec() function checks the

status of the TX_Idle flag bit and restarts the

transmitter if necessary.

6. References

1. Takashi Kenjo, “Stepping motors and their

Microprocessor Controls”, Oxford University Press,

1984.

2. Ken Berringer, “Linear Velocity Control of Stepper

Motors”,

Incremental Motion Systems Symposium, June 1999

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