Kawasaki 80C152 - Manual (Page 96)

KS152JB Universal Communications Controller
Technical Specifications
Kawasaki LSI USA, Inc. Page 96 of 120 Ver. 0.9 KS152JB2
It is recommended that user software should never write 1s to unimplemented bits in MCS-51
devices. Further versions of the device may have new bits installed in these locations. If so, their
reset value will be 0. Old software that writes 1s to newly implemented bits may unexpectedly
invoke new features.
The MCS-51 interrupt structure provides hardware support for only two priority levels, High and
Low. With as many interrupt sources as the 8XC152 has, it may be helpful to know how to aug-
ment the priority structure in the software. Any number of priority levels can be implemented in
software by saving and redefining the interrupt enable registers within the interrupt service rou-
tines.
5.1 GSC Transmitter Error Conditions
The GSC Transmitter section reports three kinds of error conditions:
TCDT - Transmitter Collision Detector
UR - Underrun in Transmit FIFO
NOACK - No Acknowledge
These bits reside in the TSTAT register. User software can read them, but only the GSC hardware
can write to them. The GSC hardware will set them in response to the various error conditions that
they represent. When the user software sets the TEN bit, the GSC hardware will at that time clear
these flags. This is the only way these flags can be cleared.
The logical OR of these three bits flags the GSC Transmit Error interrupt (GSCTE) and clears the
TEN bit, as shown in Figure below. Thus any detected error condition aborts the transmission. No
CRC bits are transmitted. In the SDLC mode an EOF is generated. In CSMA/CD mode an EOF is
generated by default, since the GTXD pin is pulled to a logic 1 and held there.
The TCDT bit can get set only if the GSC is configured to CSMA/CD mode. In that case the GSC
hardware sets the TCDT when a collision is detected during a transmission, and the collision was
detected after TFIFO has been accessed. Also, the GSC hardware sets TCDT when a detected col-
lision causes the TCDCNT register to overflow.
TCDT
UR
NOACK
TEN
TRANSMIT
EOF
GSCTE
Clear
TEN
Set
TDN
Transmit Error Flags (Logic for Clearing TEN, Setting TDN)