260
Am79C973/Am79C975
P R E L I M I N A R Y
SMIU Command Register (MReg Address 31)
Bit No.
Name and Description
7
MIRQEN
Default: 0
Read/Write
MIRQEN allows the MIRQ pin to be active if
the interrupt flag MIRQ in the SMIU Interrupt
register is set. If MIRQEN is cleared to 0, the
MIRQ pin will be disabled regardless of the
state of MIRQ. MRIRQEN is cleared by
H_RESET.
6
MTX_DONEM
Default: 0
Read/Write
If MTX_DONEM is set to a 1, the MTX_DONE
bit in the SMIU Interrupt register will be
masked and unable to set the MIRQ bit.
MTX_DONEM is cleared by H_RESET.
5
MRX_DONEM
Default: 0
Read/Write
If MRX_DONEM is set to a 1, the MRX_DONE
bit in the SMIU Interrupt register will be
masked and unable to set the MIRQ bit.
MRX_DONEM is cleared by H_RESET.
4
RESERVED
Default: 0
Read/Write as ZERO only
Reserved bit. For future use only
3
MLOOP
Default: 0
Read/Write
If MLOOP is set to 0, transmit frames will be
blocked from being received back, in case the
transceiver loops back the data. Setting
MLOOP to 1 enables loopback mode. All data
that is transmitted will be received back, if the
transceiver loop backs the data and the data
passes the acknowledgment frame filter. The
transceiver loopback can be achieved by pro-
gramming the device into loopback mode or by
using an external loopback connector. MLOOP
has no effect., when the Am79C975 controller
is configured for full-duplex operation. Re-
ceives are never blocked in full-duplex mode.
MLOOP is cleared by H_RESET.
2
MRX_RPA
Default: 0
Read/Write
When MRX_RPA is set to a 1, the Am79C975
controller will accept runt frames (frames
shorter than 64 bytes) that pass the acknowl-
edgment frame filter. MRX_RPA is cleared by
H_RESET.
1:0
RESERVED
Default: 00
Read/Write as ZERO only
Reserved bits. For future use only
SMIU Interrupt Register (MReg Address 32)
Bit No.
Name and Description
7
MIRQ
Default: 0
Read clear, write has no effect.
MIRQ indicates that one of the following inter-
rupt
causing
conditions
MTX_DONE or MRX_DONE and the associat-
ed mask bit is programmed to allow the event
to cause an interrupt. If the MIRQEN bit in the
SMIU Command register is set to 1 and MIRQ
is set, the MIRQ pin will be active. MIRQ is
cleared by clearing all the active individual in-
terrupt bits that have not been masked out, i.e.
MIRQ will clear after reading the Interrupt reg-
ister. MIRQ is also cleared by H_RESET.
has
occurred:
6
MTX_DONE
Default: 0
Read clear, write has no effect.
MTX_DONE is set by the Am79C975 control-
ler after an alert frame has been transmitted.
When MTX_DONE is set, the MIRQ pin is as-
serted if MIRQEN is set to a 1 and the mask bit
MTX_DONEM in the SMIU Command register
is 0. MTIRQ is automatically cleared after
reading the Interrupt register. MTX_DONE is
also cleared by H_RESET.
5
MRX_DONE
Default: 0
Read clear, write has no effect.
MRX_DONE is set by the Am79C975 control-
ler after an acknowledgment frame has been
received. When MRX_DONE is set, the MIRQ
pin is asserted if MIRQEN is set to a 1 and the
mask bit MRX_DONEM in the SMIU Com-
mand register is 0. MRX_DONE is automati-
cally cleared after reading the Interrupt
register. MRX_DONE is also cleared by
H_RESET.
4:0
RESERVED