CS8920A View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
'CS8920A' PDF : 144 Pages View PDF
CS8920A
6.0 TEST MODES
Loopback & Collision Diagnostic Tests
Internal and external Loopback and Collision
tests can be used to verify the CS8920A’s func-
tionality when configured for either 10BASE-T
or AUI operation.
Internal Tests
Internal tests allow the major digital functions to
be tested, independent of the analog functions.
During these tests, the Manchester encoder is
connected to the decoder. All digital circuits are
operational, and the transmitter and receiver are
disabled.
External Tests
External test modes allow the complete chip to
be tested without connecting it directly to an
Ethernet network.
Loopback Tests
During Loopback tests, the internal Carrier Sense
(CRS) signal, used to detect collisions, is ig-
nored, allowing packet reception during packet
transmission.
10BASE-T Loopback and Collision Tests
10BASE-T Loopback and Collision Tests are
controlled by two bits: Force FDX (Register 1D,
AutoNegCTL, Bit F) and ENDECloop (Register
19, TestCTL, Bit 9). Table 6.1 describes these
tests.
AUI Loopback and Collision Tests
AUI Loopback and Collision tests are controlled
by two bits in the Test Control register: AUIloop
(Register 19, TestCTL, Bit A) and ENDECloop
(Register 19, TestCTL, Bit 9). Table 6.2 de-
scribes these tests.
Test Mode
10BASE-T Internal
Loopback
10BASE-T
Internal
Collision
10BASE-T
External Loopback
10BASE-T
External
Collision
FDX
1
0
1
0
ENDECloop
Description of Test
1
Transmit a frame and verify that the frame is received without error.
1
Transmit frames and verify that collisions are detected and that
internal counters function properly. After 16 collisions, verify that
16coll (Register 8, TxEvent, Bit F) is set.
0
Connect TXD+ to RXD+ and TXD- to RXD-. Transmit a frame and
verify that the frame is received without error.
0
Connect TXD+ to RXD+ and TXD- to RXD-. Transmit frames and
verify that collisions are detected and that internal counters function
properly. After 16 collisions, verify that 16coll (Register 8, TxEvent,
Bit F) is set.
Table 6.1. 10BASE-T Loopback and Collision Tests
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