am79c940 Advanced Micro Devices, am79c940 Datasheet - Page 20

• Manufacturer Part Number: am79c940
• Description: Media Access Controller For Ethernet Mace
• Manufacturer: Advanced Micro Devices

TXEN/TXEN
Transmit Enable (Output)
When the AUI port is selected (PORTSEL [1–0] = 00),
an output indicating that the AUI DO differential output
has valid Manchester encoded data is presented. When
the 10BASE-T port is selected (PORTSEL [1–0] = 01),
indicates that Manchester data is being output on the
TXD /TXP
port is selected (PORTSEL [1–0] = 10), indicates that
Manchester data is being output on the DAI
TXDAT complementary outputs. When the GPSI port
is selected (PORTSEL [1–0] =11), indicates that NRZ
data is being output from the MAC core of the MACE de-
vice, to an external Manchester encoder/decoder, on
the TXDAT+ output. Active low when the DAI port is se-
lected, active high when the AUI, 10 BASE-T or GPSI is
selected. Operates at TTL levels.
RXDAT
Receive Data (Input)
When the DAI port is selected (PORTSEL [1–0] = 10),
the Manchester encoded data input to the integrated
clock recovery and Manchester decoder of the MACE
device, from an external network transceiver. When the
GPSI port is selected (PORTSEL [1–0] =11), the NRZ
Notes:
1. PORTSEL [1–0] and ENPLSIO are located in the PLS Configuration Control register (REG ADDR 14).
2. When the GPSI port is selected, TXEN should have an external pull-down attached (e.g. 3.3k ) to ensure the output is held
3. This pin should be externally terminated, if unused, to reduce power consumption.
20
Notes:
1. PORTSEL [1–0] and ENPLSIO are located in the PLS Configuration Control register (REG ADDR 14).
2. This pin should be externally terminated, if unused, to reduce power consumption.
inactivebefore ENPLSIO is set.
SLEEP
SLEEP
AMD
0
1
1
1
1
1
0
1
1
1
1
1
complementary outputs. When the DAI
PORTSEL
PORTSEL
[1–0]
[1–0]
XX
XX
XX
XX
00
01
10
11
00
01
10
11
ENPLSIO
ENPLSIO
X
X
1
1
1
1
0
1
1
1
1
0
TXEN/TXEN Configuration
RXDAT Configuration
port
Am79C940
Interface Description
Interface Description
Sleep Mode
AUI
10BASE-T
DAI Port
GPSI
Status Disabled
Sleep Mode
AUI
10BASE-T
DAI Port
GPSI
Status Disabled
decoded data input to the MAC core of the MACE de-
vice, from an external Manchester encoder/decoder.
Operates at TTL levels.
RXCRS
Receive Carrier Sense (Input/Output)
When the AUI port is selected (PORTSEL [1–0] = 00),
an output indicating that the DI input pair is receiving
valid Manchester encoded data from the external trans-
ceiver which meets the signal amplitude and pulse width
requirements. When the 10BASE-T port is selected
(PORTSEL [1–0] = 01), an output indicating that the
RXD input pair is receiving valid Manchester encoded
data from the twisted pair cable which meets the signal
amplitude and pulse width requirements. RXCRS will be
asserted high for the entire duration of the receive mes-
sage. When the DAI port is selected (PORTSEL [1–0] =
10), an input signaling the MACE device that a receive
carrier condition has been detected on the network, and
valid Manchester encoded data is being presented to
the MACE device on the RXDAT line. When the GPSI
port is selected (PORTSEL [1–0] = 11), an input signall-
ing the internal MAC core that valid NRZ data is being
presented on the RXDAT input. Operates at TTL levels.
High Impedance
TXEN Output
TXEN Output
TXEN Output
TXEN Output
High Impedance (Note 3)
High Impedance
High Impedance (Note 2)
High Impedance (Note 2)
RXDAT Input
RXDAT Input
High Impedance (Note 2)
Pin Function
Pin Function