MC68LC302 Datasheet, PDF (85/169 Pages) Motorola, Inc – Low Power Integrated Multiprotocol Processor Reference Manual

Communications Processor (CP)
• Case 2– As each character is assembled, it is stored into a complete byte. Assuming
that the characters are ASCII characters with 7-bit codes, the 8th bit of the byte will con-
tain the parity bit. If the parity is either even or odd, then after receiving an odd character
and an even character, the 8th bit should be different for the odd and even characters.
The parity can be determined by the setting of the parity bit for one of the two charac-
ters. If the 8th bit is always a 1, this is the same as a 7-bit character, no parity and at
least 2 STOP bits or a 7-bit character with force 1 parity. If the 8th bit is always a zero,
then either the character is a 7-bit character with force 0 parity, or the character is a 8-
bit character with no parity.
• Case 3– This case is the same as 7-bit character with force 0 parity. The 8th bit of the
byte will always be zero.
• Case 4–This case assumes a 8-bit character with the 8th bit of the character equal to a
0 (ASCII character codes define the 8th bit as zero). If the parity is either even or odd,
then after receiving an odd and an even character, a framing error (FE) interrupt should
have been generated for one of them (the interrupt is generated when the parity bit is
zero). The user can determine the parity by which character generated a FE interrupt
(if the odd character did, then the parity is odd). If a framing error occurs on every char-
acter, then the character is 8-bits with force 0 parity. If no framing error occurs, than this
is the same as Case 5.
• Case 5– This case is not supported, because it can not be differentiated from 7-bit force
0 parity and 8-bit no parity. If the 9th bit is a 1, then it will be interpreted as a STOP bit.
4.3.9.7 AUTOBAUD RECEPTION ERROR HANDLING PROCEDURE. The autobaud
controller reports reception error conditions using the autobaud command descriptor. Three
types of errors are supported:
• Carrier Detect Lost during reception
When this error occurs and the channel is not programmed to control this line with software,
the channel terminates reception, sets the carrier detect lost (CD) bit in the command
descriptor, and generates the CCR interrupt, if enabled. CCR is bit 3 of the SCCE register.
• Overrun Error
When this error occurs, the channel terminates reception, sets the overrun (OV) bit in the
command descriptor, and generates the CCR interrupt, if enabled.
• End Of Table Error
When this error occurs, the channel terminates reception, sets the end of table (EOT) bit in
the command descriptor, and generates the CCR interrupt, if enabled.
Any of these errors will cause the channel to abort reception. In order to resume autobaud
operation after an error condition, the M68000 should clear the status bits and issue the
Enter_Baud_Hunt command again.
4.3.9.8 AUTOBAUD TRANSMISSION. The autobaud package supports two methods for
echoing characters or transmitting characters. The two methods are automatic echo and
smart echo.
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MC68LC302 REFERENCE MANUAL
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