mc68194 ON Semiconductor, mc68194 Datasheet - Page 18

• Manufacturer Part Number: mc68194
• Description: Carrier Band Modem Cbm
• Manufacturer: ON Semiconductor

8.1 OVERVIEW
commands on the request channel: RESET, DISABLE
LOOPBACK, ENABLE TRANSMITTER, and IDLE. The
serial data station management commands are not
implemented in the MC68194. These unimplemented
commands are typically used to set up and read registers or
control bits within a more complex modem. The CBM does
not have registers and does not require the SMDATA
commands. Upon reception of a SMDATA command, the
CBM will respond with a NONACKNOWLEDGEMENT
(NACK) and a response byte in accordance with the IEEE
DTE−DCE Interface Standard. The data in the response byte
is all ZEROs. Receipt of a RESET, DISABLE LOOPBACK,
or ENABLE TRANSMITTER command will abort the
SMDATA response.
8.2 RESET
RESET pin; the internal loopback mode is enabled, the
transmitter outputs are disabled and TXDIS is enabled, and
the jabber inhibit timeout is cleared. In addition the RESET
command will generate an ACKNOWLEDGEMENT
response (ACK) on the RXSYMx pins.
high it resets the CBM as described above leaving the CBM
ready to respond to the physical data request channel.
commands after a hardware reset, the request channel must
either be in MAC mode upon exiting the hardware reset or
the request channel must go to MAC mode briefly before
going to management mode. If the MC68194 is in
management mode upon exiting the hardware reset, it
remains reset and does not recognize the command because
it is waiting for a MAC mode to management mode
transition. This situation can be corrected by either exiting
hardware reset with the request channel in MAC mode or
putting the request channel in MAC mode briefly before
issuing any management commands. See Section 8.6 for
command response timing.
8.3 INTERNAL LOOPBACK
CBM. In this mode a multiplexer selects the internal
transmitter signal to drive the clock recovery and data
recovery portions of the receive circuitry. This transmit
signal is taken just prior to the output buffer stages of the
transmitter circuit.
(management command or external pin). Loopback mode is
exited upon receipt of the management command
DISABLE LOOPBACK. The CBM will respond with ACK
to this command.
The MC68194 supports four physical management
The RESET command performs the same function as the
The RESET pin is an asynchronous function. When taken
NOTE: For the MC68194 to respond properly to
The internal loopback mode is provided for testing the
The loopback mode can only be selected via RESET
PHYSICAL MANAGEMENT
http://onsemi.com
SECTION 8
18
be:
1. Initialize the CBM via a RESET command or hardware
2. Return to MAC mode and send test data. The CBM is full
3. In management mode, send DISABLE LOOPBACK
operation.
8.4 STANDARD OPERATION
enabled as well as disabling loopback. The transmitter is
automatically disabled on RESET. Three things must
happen after a RESET before transmissions can begin:
1. Loopback mode must be exited with the DISABLE
2. The transmitter must be activated with the ENABLE
3. The MC68194 must exit the management mode and
CBM is in MAC or data mode, loopback is disabled, and the
transmitter is enabled.
8.5 IDLE
management command is received. In addition, the IDLE
response is returned for all invalid, as opposed to
unimple−mented (SMDATA) commands.
8.6 COMMAND RESPONSE TIMING
operation is:
1. ACK response to RESET, DISABLE LOOPBACK, and
2. The IDLE command and all invalid commands will
3. The SMDATA command response timing is shown in
A normal sequence of events to test the CBM then would
Following the test the modem can be setup for standard
Standard operation requires that the transmitter be
The CBM is now ready to send and receive data, i.e., the
The CBM provides the IDLE response when an IDLE
The
reset.
duplex.
command to exit loopback.
LOOPBACK command. The MC68194 responds to this
command with the ACK management response.
TRANSMITTER command. The MC68194 responds to
this command with the ACK management response.
enter the MAC data mode.
ENABLE TRANSMITTER within 2 clock periods. As
shown in Figure 8−1, the precise response time depends
on the relative phase of the TXCLK and the RXCLK
signals. If they are in phase, the response will be
available at the RXSYMx pins 1.5 clocks after the
command is latched. If the clocks are 180° out of phase,
the delay will be 2 clocks. The command should be held
on the TXSYMX pins until the response is received on
the RXSYMX pins.
produce the IDLE response with the same delay as
described above.
Figure 8−2. The NACK response to the SMDATA
command is available on the RXSYMX pins in 2.5 or 3
MC68194’s
management
command/response