mc68194 ON Semiconductor, mc68194 Datasheet - Page 19

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

TXCLK. These clocks may be in phase or 180° out of phase
as discussed above. This uncertainty exists because the
clock recovery PLL can lock to either phase of the local
clock. The response delays relative to TXCLK may
therefore differ by 1/2 clock period. The MC68194 must
leave management mode, enter MAC mode, and return to
management mode for a phase change to occur. The relative
phase of the two clocks will not change while in
management mode.
when first entering management mode, the PLL must have
In management mode, RXCLK is always locked to
Because the clock recovery PLL requires a training period
clock periods depending on the relative phases of the
TXCLK and RXCLK signals. When NACK becomes
valid, RXSYM0 is low creating a start bit for the
response byte. NACK is held for 9 clock periods with
RXSYM0 low (start bit plus 8 ZERO data bits). NACK
is held for one additional clock with RXSYM0 high. This
is the stop bit and mark the end of the SMDATA response
byte. 12.5 or 13 clock periods after receiving the
SMDATA command the NACK response is removed.
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sufficient time to lock to the new clock source (TXCLK)
before being required to provide a response. To provide
enough time for the PLL to lock up, the MC68194 delays
16.5 to 17 clock periods before entering station management
mode (SMIND* = 0) after the station management mode is
selected (SMREQ* = 0). Refer to Figure 8−3 for the timing
diagram. During this delay, the MAC mode SILENCE
response will be present on the RXSYMX pins.
management mode there will be this added delay before the
mode is entered and a response is available. If a management
command is sent along with the station management mode
request (SMREQ* = 0) and held on the TXSYMX pins until
the CBM enters station management mode, the proper
response will be available on the RXSYMX pins
immediately except in the case of SMDATA commands.
SMDATA commands must not be requested on the
TXSYMX pins until after SMIND* indicates that station
management mode has been entered.
Users must be aware that when first requesting