
C165H
IOM-2 Interface Controller
Data Sheet
338
2001-04-19
PRELMNARY
XTF
as soon as the selected buffer size in the FIFO is available
-EXCERPT-
after the successful transmission of the closing flag. The transmitter
sends always an abort sequence
holds no further transmit data. This occurs if the host fails to respond to an XPR
interrupt quickly enough.
–
XMR
(
T
ransmit
M
essage
R
epeat) interrupt, indicating that the transmission of the
complete last frame has to be repeated as, for example, a collision on the S bus has
been detected.
Three different control commands are used for transmission of data:
–
XTF
(
T
ransmit
T
ransparent
F
rame) command, telling the HDLC controller that a word/
byte has been written to the TFIFO and should be transmitted. A start flag is generated
automatically.
–
XME
(
T
ransmit
essage
nd) command, telling the HDLC controller that the last data
written to the TFIFO completes the corresponding frame and should be transmitted.
This implies that according to the selected mode a frame end (CRC + closing flag) is
generated and appended to the frame.
–
XRES
(
T
ransmitter
eset) command, resetting the HDLC transmitter and clearing the
transmit FIFO of any data.
Optionally one additional status conditions can be read by the host:
–
XDOV
(
T
ransmit
D
ata
O
verflow), indicating that the data block size has been
exceeded, i.e. CPU writes to an occupied TFIFO.
The TFIFO requests service from the microcontroller by setting a bit in the ISTAH
register, which causes an interrupt (XPR, XDU, XMR). The microcontroller can then read
the status register STAR (XDOV) and write data in the FIFO.
The instant of the initiation of a transmit pool ready (XPR) interrupt after different transmit
control commands is listed in
Table 68
.
When setting XME the transmitter appends the FCS and the endflag at the end of the
frame. When XTF & XME has been set, the TFIFO is locked until successful
transmission of the current frame, so a consecutive XPR interrupt also indicates
successful transmission of the frame whereas after XME or XTF the XPR interrupt is
Table 68
XPR Interrupt (availability of the TFIFO) after XTF, XME
Commands
CMDR.
Transmit pool ready (XPR) interrupt initiated...
XTF &
XME