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PEB 20321
PEF 20321
Host Memory Organization
Data Sheet
305
2001-02-14
The Rx Descriptor is accessed in the following order (assuming a normal complete
access with HOLD =
‘
0
’
, i.e. no polling):
1. Access n:
Read the first descriptor DWORD
2. Access n + 1:
Read the next Rx descriptor pointer
3. Access n + 2:
Read the Rx data pointer
4. Access n + 3:
Write the current Rx descriptor address to Control and Configuration
Block (CCB)
5. Access n + 4:
Data Transfer
6. Access n + 5:
Write the fourth descriptor DWORD (number of received data bytes,
status information)
7. Access n + 5:
Handle selected interrupts
Note: The MUNICH32X does
not
update the fourth DWORD if the receive initialization
command is used during normal operation (see
Chapter 12.5
)
The descriptor bit fields have the following meaning:
HOLD:
Setting the HOLD bit by the host prevents the device from branching to the
next descriptor. The current data section is still filled.
–
Afterwards the fourth descriptor DWORD is written by the MUNICH32X.
For HDLC, TMB, TMR the FE and C bits are set. If the frame could not
completely be stored into the data section the RA bit is set in the status.
An interrupt with set FI bit is generated, and in case the frame was aborted,
the ERR bit is also set.
For TMA, V.110/X.30 the C bit and the RA bit are set and an interrupt with
set ERR but with FI =
‘
0
’
is generated.
–
Afterwards the device starts polling the HOLD bit. Received data and
received events normally leading to interrupts (with RT = 1) are discarded
until HOLD =
‘
0
’
is detected. Each 1
…
4 byte data word or interrupt event
normally leading to an access now results in a poll cycle.
Whenever HOLD =
‘
1
’
is detected the next Rx descriptor address is read
but ignored.
–
When HOLD =
‘
0
’
is detected
for HDLC, TMB, TMR the device continues to discard data until the end
of a received frame or an event leading to an interrupt (with RT =
‘
1
’
) is
detected. Afterwards the next received frame is transferred into the next
Rx descriptor. Interrupts are also generated again.
For V.110/X.30, TMA the device puts the next data into the next Rx
descriptor. Interrupts are also generated again.
The HOLD condition is also discarded upon detection of a receive jump, fast
receive abort or receive initialization command. The MUNICH32X then
branches to the Rx descriptor determined by FRDA even though the HOLD
bit in the current Rx descriptor may still be
‘
1
’
.