© MCS Electronics, 1995-2007

'stored in a buffer. This way you will not loose characters providing that 'you empty the buffer

'So when you fast type abcdefg, they will be printed after each other with the '1 second delay

'Using the CONFIG SERIAL=BUFFERED, SIZE = 10 for example will 'use some SRAM memory

'The following internal variables will be generated :

CONFIG SERIALIN1

Action

Configures the second hardware UART to use a buffer for input

Syntax

CONFIG SERIALIN1 = BUFFERED , SIZE = size [,CTS=pin, RTS=pin , Threshold_full=num , Threshold_empty=num ]

Remarks

The following internal variables will be generated : _RS_HEAD_PTR1 , a byte counter that stores the head of the buffer _RS_TAIL_PTR1 , a byte counter that stores the tail of the buffer.

_RS232INBUF1 , an array of bytes that serves as a ring buffer for the received characters. _RS_BUFCOUNTR1, a byte that holds the number of bytes that are in the buffer.

To clear the buffer, use CLEAR SERIALIN1. Do not read and write the internal buffer variables yourself.

CTS-RTS is hardware flow control. Both the sender and receiver need to use CTS-RTS when CTS-RTS is used. When on of the partie's does not use CTS-RTS, no communication will be possible.

CTS-RTS use two extra lines. The receiver must check the CTS pin to see if it may send. The CTS pin is a input pin as the receiver looks at the level that the sender can change.

The receiver can set the RTS pin to indicate to the sender that it can accept data.

In the start condition, RTS is made '0' by the receiver. The sender will then check this logic level with it's cts pin, and will start to send data. The receiver will store the data into the buffer and when the buffer is almost full, or better said, when the Threshold_ful is the same

page -375-

© MCS Electronics, 1995-2007

_RS232OUTBUF0, array of bytes for the ring buffer that stores the printed data. _RS_BUFCOUNTW0, a byte that holds the number of bytes in the buffer.

Serial buffered output can be used when you use a low baud rate. It would take relatively much time to print all data without a buffer. When you use a buffer, the data is printed on the background when the micro UART byte buffer is empty. It will get a byte from the buffer then and transmit it.

As with any buffer you have, you must make sure that it is emptied at one moment in time. You can not keep filling it as it will become full. When you do not empty it, you will have the same situation as without a buffer !!! When the roof is leaking and you put a bucket on the floor and in the morning you empty it, it will work. But when you will go away for a day, the bucket will overflow and the result is that the floor is still wet.

Another important consideration is data loss. When you print a long string of 100 bytes, and there is only room in the buffer for 80 bytes, there is still a wait evolved since after 80 bytes, the code will wait for the buffer to become empty. When the buffer is empty it will continue to print the data. The advantage is that you do not loose any data, the disadvantage is that it blocks program execution just like a normal un-buffered PRINT would do.

ASM

Routines called from MCS.LIB :

_CHECKSENDCHAR. This is an ISR that gets called when ever the transmission buffer is empty.

Since UDRE interrupt is used , you can not use this interrupt anymore. Unless you modify the _CheckSendChar routine of course.

When you use the PRINT statement to send data to the serial port, the UDRE interrupt will be enabled. And so the _CheckSendChar routine will send the data from the buffer.

See also

CONFIG SERIALIN

Example

page -378-