Indication Channel Encodings For Mac Mode (Smind = 1) - Motorola MC68824 User Manual

SYMBOL
TXSYM2 TXSYMI TXSYMO
RESET
1 1 1
LOOPBACK OISABLE 1 0 1
ENABLE TRANSMITIER 0 1 1
SERIAL SM DATA ZERO
0 0 0
OR START BIT
SERIAL SM DATA ONE 0 0 1
OR STOP BIT OR IDLE
Figure 5-5. Request Channel Encodings for Station
Management Mode (SMREQ
=
0)
5.6.2 Physical Data Indication Channel
Five input signals comprise the physical data indication channel. Three of these signals are mul-
tiplexed and have different meanings depending on the mode of operation. The SMIND signal
determines if the channel is in station management mode or MAC mode. When programmed for
MAC operation, this channel is used by the physical layer to provide encoded indications of the
data unit reception. In station management mode, this channel either carries confirmations to
commands passed to the physical layer or reports physical layer conditions.
5.6.2.1 STATION MANAGEMENT INDICATION (SMIND). SMIND is an input to the TBC which
indicates whether the physical layer is in MAC mode (SMIND=O) or station management mode
(SMIND = 1). SMIND is called RXSYM3 in the 802.4G Draft Standard. When in MAC mode, the
physical layer sends encoded indications of data unit reception (silence, non-data, bad signal,
data 'one', and data 'zero'). The physical layer enters management mode (SMIND=O) to send
responses to management commands at the request of the TBC, to report an error event at the
initiative of the modem, or to report real time data also at the initiative of the modem.
5.6.2.2 RECEIVE CLOCK (RXCLK). The receive clock is supplied to the TBC by the physical layer
and can be from 10 kHz to 16.67 MHz. RXSYMO, RXSYM1, RXSYM2, and SMIND are synchronized
to RXCLK.
5.6.2.3 RXSYMO, RXSYM1, AND RXSYM2 IN MAC MODE. Figure 5-6 shows the encoding of
RXSYMO, RXSYM 1, and RXSYM2 in MAC mode.
SYMBOL RXSYM2
DATA ZERO
0
DATA ONE 0
BAD-SIGNAL 0
NON-DATA 1
SILENCE 1
Where:
DATA ZERO is a binary zero
DATA ONE is a binary one
RXSYMI RXSYMO
0 0
0 1
1 X
0
X
1 X
BAD-SIGNAL indicates reception of a bad signal for one MAC symbol
period
NON-DATA is a delimiter flag. In the absence of errors, NON-DATA
will always be present in pairs
SILENCE is silence or pseudo-silence for one MAC symbol period
MC68824 USER'S MANUAL
Figure 5-6. Indication Channel Encodings for
MAC Mode (SMIND
=
1)
MOTOROLA
5-7
II