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73Am79C930
to TIR10. It is also possible to use 80188 MOV instruc-
tions to unload RX data from the RX FIFO. The RX FIFO
may be unloaded by reading from TIR18.
DMA Channel Allocation In The 80188 Core
80188 DMA Channel DMA Request Source
DRQ0 TAI RX FIFO NOT EMPTY
DRQ1 TAI TX FIFO NOT FULL
Loopback Operation
The Am79C930 device contains a loopback mode that
is invoked by writing a 1 to the LOOPB bit of TCR3[7].
When LOOPB is set to a 1, then the Am79C930 device
will perform an internal loopback of all transmissions.
The data path transmitted will move out of the TX FIFO
and be serialized.
Use of shared resources can be controlled by the order
of writing to the TXS and RXS bits of TIR8 and TIR16,
respectively. The bit (of TXS and RXS) that is set last
will determine the owner of the SFD detection logic
shared resource.
LED Support
Two pins are provided with the necessary drive capabil-
ity to directly drive a standard indicator LED. The output
value for these pins is directly programmable through
TIR register bits that are accessible to both the 80188
embedded core through the memory interface and to
the driver software through the system interface. These
two pins are also programmable as inputs so that alter-
native functionality may be defined for these pins.
RESET Methods
There are multiple reset conditions that can be
applied to the Am79C930 device. Each of the reset con-
ditions and its effect on the device are indicated in the
following sections.
RESET Pin
There is a single RESET input to the Am79C930 device.
When the RESET pin is asserted for the specified mini-
mum time and then the RESET pin is deasserted, gen-
erally speaking, all major state machines in the
Am79C930 device and all registers in the Am79C930
device are reset to their default values, with the excep-
tions noted below.
The following registers and state machines are RESET
to their default values by assertion of the RESET pin:
(Note that some register locations’ default values
are UNDEFINED):
All SIR registers,
except
SIR2[7:0] and
SIR3[6:0], which are unaffected.
All MIR registers.
All TIR registers.
All TCR registers.
All TAI state machines.
All PCMCIA registers.
All ISA PnP registers.
The ISA PnP state machine is returned to its
idle state.
The 80188 controller is held in RESET as long as the
RESET pin is held asserted.
The sleep state machine is returned to its idle state
(i.e., awake).
The memory bus arbitration state machine is re-
turned to its idle state.
The BIU will be reset to an inactive state, such that all
tri-stateable outputs will be put into a high-impedance
state. The internal slave state machine will revert to the
idle state; any slave operation that was in progress at
the time of the RESET operation will be abruptly discon-
tinued. The BIU will recognize a new slave access from
the host beginning four CLKIN clocks of the deassertion
of the RESET pin.
The embedded 80188 controller will be reset by the as-
sertion of the RESET pin, provided that the minimum
pulse width requirement for the RESET signal is met.
Any TX or RX operation that was in progress at the TAI
at the time of the RESET assertion will be discontinued
abruptly. All RX and TX FIFO data will remain in the
FIFOs. RX and TX FIFOs can only be cleared by asser-
tion of the RXFR and TXFR bits of TIR16 and TIR8. TAI
Unit will not resume TX and RX operations until the
80188 core instructs it to do so.
SWRESET (SIR0[7])
The SWRESET bit of SIR0[7] can be used to reset the
system interface section of the Am79C930 device.
When the SWRESET bit is asserted, then the BIU sec-
tion of the Am79C930 device will be reset, including the
arbitration state machine that translates 80188 cycles
into memory bus cycles.
The following registers and state machines are RESET
to their default values by assertion of the SWRESET bit
of SIR0[7]:
(Note that some register locations’ default values
are UNDEFINED):
All SIR registers,
except
SIR0[7] and all of SIR2[7:0]
and SIR3[6:0] which are unaffected.
All MIR registers.