AMD AMD5K86 - BOFF (Backoff)

AMD~
18524B/O-Mar1996 AMD5tfJ6 Processor Technical Reference Manual
5.2.9 BF (Bus Frequency)
Summary
Sampled
Details
Signal Descriptions
Input
During RESET, BF selects between a high and low multiplica-
tion factor for the frequency ratio between the processor's
internal clock and the bus clock (CLK).
The processor samples BF only on the falling edge of RESET.
The signal assertion must be stable 10 clocks prior to its sam-
pling. BF
has a weak internal pullup resistor; see the data
sheet for details.
Table 5-7 shows the ratios between the processor clock and the
bus clock (CLK) for the High and Low values of BF. BF may be
tied High or Low. Due to the internal pullup resistor, the lower
ratio is selected if BF is left unconnected.
TABLE 5-7. Processor-to-Bus Clock Ratios
State of BF Input
Processor-Clock to Bus-Clock Ratio
BF= 1
L5x
BF=O 2.0x
Notes:
I.
The default processor-to-clock ratios are shown in Table 5-7. Specific mod-
els of the AMD5,!36 processor may implement different ratios for the Ht
and Low values of BF. For authorative information, see the data sheet or
each AMD5,!36 processor model
5-31