C541U_99 Datasheet, PDF (147/192 Pages) Siemens Semiconductor Group – 8-BIT CMOS MICROCONTROLLER

Interrupt System
C541U
The register EPIRn (n=0-4) contaíns USB endpoint specific interrupt request flags. This SFR is
availble for each endpoint. If a request flag in EPIRn is set, it is automatically cleared after a read
operation of the EPIRn register.
Endpoint Interrupt Request Register EPIRn, n=0-4 (Address C4H) Reset Value EPIR0 : 11H
Reset Value EPIR1 to EPIR4 : 10H
Bit No.
C4H
MSB
7
6
5
4
3
2
1
ACKn NACKn RLEn
–
DNRn NODn EODn
r
r
r
r
r
r
r
For accessing EPIRn, SFR EPSEL must be 0nH.
LSB
0
SODn
r
EPIRn
Bit
ACKn
NACKn
RLEn
–
DNRn
NODn
EODn
SODn
Function
USB acknowledge
Bit ACKn=1 indicates a succesful action on the USB.
USB not acknowledge
Bit NACK is set for all unsuccessful actions on the USB.
Read length error
Bit RLEn is automatically set if the number of bytes read by the USB does not
correspond to the packet length programmed by the CPU.
Reserved bit for future use;
Data not ready
This bit is set by hardware if the USB module requires an access to USB
memory, but no buffer is available.
No data
This bit indicates an incorrect CPU read or write access to USB memory.
End of data
During an USB read access EOD is set if the CPU has written a
programmable number of bytes in the transmit buffer. During an USB write
access EOD is set if the CPU has read a programmable number of bytes out
of the receive buffer.
Start of data
During an USB read access SOD is set if the USB has read a fixed number of
bytes from the transmit buffer. During an USB write access SOD is set if the
USB has written a fixed number of bytes to the receive buffer.
Semiconductor Group
7-14
1997-10-01