AM8530H AMD [Advanced Micro Devices], AM8530H Datasheet - Page 45

• Manufacturer Part Number: AM8530H
• Description: Serial Communications Controller
• Manufacturer: AMD [Advanced Micro Devices]

AMD
In External Sync Mode, the SYNC/HUNT status bit, as in Asynchronous mode, reports
the state of the SYNC pin. If there are no other External/Status interrupts pending, then
any transition on the SYNC pin will cause the latches to close and generate an External/
Status interrupt. However, only an odd number of transitions on SYNC, while another Ex-
ternal/Status interrupt is pending, will close the latches and generate an External/Status
Interrupt.
3.8.2
The BREAK/ABORT status bit is used in Asynchronous and SDLC modes but is always
set to ‘0’ in Synchronous modes. Both a Low-to-High and High-to-Low transition are guar-
anteed to cause the External/Status latches to close, and if the BREAK/ABORT IE bit in
WR15 is set to ‘1’, generate an External/Status interrupt regardless of whether another
External/Status interrupt is pending at the time the transitions occur. If BREAK/ABORT is
detected while the latches are closed, the status will be saved and generate an interrupt
for BREAK/ABORT detection upon issuing the Reset External/Status Interrupts. A second
interrupt is generated for End of BREAK/ABORT after issuig the next Reset External/
Status Interrupts. In the first case, the BREAK/ABORT bit will be set to ‘1’, and in the sec-
ond case to ‘0’. This will guarantee that the BREAK/ABORT sequence is detected cor-
rectly. A BREAK/ABORT occurrence will clear an End of BREAK/ABORT that is waiting
to generate an interrupt. Therefore, multiple Break/Abort sequences while the latches are
closed will generate only two interrupts, one for BREAK/ABORT detection, and one for
End of BREAK/ABORT.
In Asynchronous mode, this bit will be set to ‘1’ when a break sequence (null character
plus Framing Error) is detected (i.e., RxD is Low for more than one full character time) in
the receive data stream, and remains set for as long as ‘0’s continue to be received. It is
reset when a ‘1’ is received. Note that a single null character is left in the Receive Data
FIFO each time a break condition is terminated. This character should be read and dis-
carded.
In SDLC mode, this status bit is set to ‘1’ when an abort sequence is detected in the re-
ceive data stream and is reset when a ‘0’ is received. Note that the receiver detects an
abort pattern whether it is “in frame” or “out of frame,” so to avoid confusion, the BREAK/
ABORT IE bit in WR15 should be set to ‘1’ in the SYNC/HUNT interrupt routine when the
SYNC/HUNT status bit indicates that the receiver is “in frame” (i.e., SYNC/HUNT status
bit transitions from High-to-Low), and should be reset to ‘0’ early in the EOF interrupt rou-
tine.
3.8.3
The Zero Count (ZC) status bit reflects when the Baud Rate Generator counter reaches a
count of ‘0’. The ZC status bit will be set to ‘1’ when the zero count is reached and will be
reset to ‘0’ when the counter is re-loaded. The External/Status latches will close only on
the Low-to-High transition of this bit and, if the Zero Count IE bit is set in WR15, generate
an External/Status interrupt. This status bit is not latched in RR0 even though the Exter-
nal/Status latches close as a result of the transition.
If there are no other External/Status interrupt conditions pending at the time the ZC status
bit is set, an External/Status interrupt will be generated. However, if there is another Ex-
ternal/Status interrupt pending at the time ZC is set, no interrupt will be generated until
the current interrupt service is complete. If the zero count condition does not persist be-
yond the end of the current interrupt service routine no interrupt will be generated. The
interrupt service routine should check the other External/Status conditions for changes. If
none changed, the ZC was the source of interrupt. In polled applications, the IP bits in
RR3A should be checked for a status change before proceeding as in the interrupt serv-
ice routine.
Note that while the Zero Count IE bit in WR15 is reset, the ZC status bit will always read
‘0’.
3–14
Break/Abort
Zero Count
I/O Programming Functional Description