AM79C930 datasheet(55/161 Pages) AMD

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P R E L I M I N A R Y

AMD

Am79C930

Diversity decision logic for determining if a satisfactory

antenna has been found. These inputs to the Stop Di-

versity decision logic are enabled by specific bits of

TCR28. The UBDSD bit of TCR28 is used to select/

deselect the Baud Determination of Stop Diversity for

use in Stop Diversity decisions and the URSSI bit of

TCR28 is used to select/deselect RSSI information in

Stop Diversity decisions. Note that the URSSI bit of

TCR28 is also used to select/deselect RSSI information

for use in CCA decisions.

The possible Stop Diversity results are shown in the

table below.

The current stop diversity result is reported in the

ANTLOK bit of TIR26.

A rising edge of ANTLOK will set the ALOKI (Antenna

Lock Interrupt = Diversity switching stopped) bit of TIR5.

This bit may serve as an interrupt to the 80188 core, or

the interrupt due to this bit may be masked and the bit

can be polled by the 80188 core.

The antenna diversity switching is signaled with the

ANTSW bit of TIR4. This bit reports a change in the an-

tenna selection. This bit may serve as an interrupt to the

80188 core, or the interrupt due to this bit may be

masked and the bit polled by the 80188 core.

The current antenna selection may be read from the

ANTSLT bit of TIR26.

The current RSSI limit comparison test result may be

read from the RSALT bit (RSSI Above Limit) of TIR28.

Automatic Antenna Diversity switching may be disabled

through appropriate setting of the ANTSEN bit of TIR26.

Manual setting of the antenna selection is then allowed

through the ANTS bit of TIR26.

TXC As Input

For typical transceiver connections, the signal TXC is

defined as an input to the transceiver. However, for

some transceiver connections, the signal TXC is de-

fined as a

transceiver output. The Am79C930 device

can accommodate both types of transceivers by allow-

ing the TXC pin to be defined as either output or input.

In the case where the TXC pin is as output from a trans-

ceiver, the TXCIN bit of TCR30 must be set to a 1 in

order to change the direction of the TXC signal. When

this is done, a 16-bit serial-FIFO is added into the path of

the TX data in order to accommodate a small amount of

possible mismatch between the transceiver’s TXC fre-

quency and the Am79C930 device’s internal TXC fre-

quency. When this FIFO is inserted into the transmit

data stream, an additional delay of 8-bit times is incurred

between the assertion of the TXS bit of TIR8 and the as-

sertion of the first transceiver transmit control signal in

the transmit control sequence.

If the mismatch between the transceiver’s TXC fre-

quency and the Am79C930 device’s TXC frequency is

too large, then a serial-FIFO overflow or underflow con-

dition may occur. When this situation arises, an error will

be indicated by the ATFO or ATFU bits of TCR11.

IEEE 1149.1 Test Access Port Interface

An IEEE 1149.1 compatible boundary scan Test Access

Port (TAP) is provided for board level continuity test and

diagnostics. All digital input, output, and input/output

pins are tested. ADREF,

TRST, TCK, TMS, TDI, TDO,

and PMX2 pins are not included in the boundary

scan test.

Stop Diversity

Baud Detect Stop

Result

UBDSD

URSSI

STPEN

Stop Diversity

RSSI >= RSSI

(ANTLOK Bit

TCR28[2]

TCR28[0]

TCR28[3]

Decision

Lower Limit

of TIR26)

don’t care

ANTLOK = FALSE

don’t care

ANTLOK = TRUE

don’t care

yes

ANTLOK = TRUE

don’t care

ANTLOK = FALSE

TRUE

don’t care

ANTLOK = TRUE

FALSE

don’t care

ANTLOK = FALSE

TRUE

yes

ANTLOK = TRUE

TRUE

ANTLOK = FALSE

FALSE

yes

ANTLOK = FALSE

FALSE

ANTLOK = FALSE

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