dsp56167 Freescale Semiconductor, Inc, dsp56167 Datasheet - Page 15

• Manufacturer Part Number: dsp56167
• Description: Advance Information 16-bit Digital Signal Processor
• Manufacturer: Freescale Semiconductor, Inc

MOTOROLA
BG
BB
Signal
Name
or Input
Output
Output
Signal
Input
Type
or
Driven
high
Input
during
Reset
State
Table 1-7 Bus Control Signals (Continued)
Bus Grant—After reset, this signal is an output (Slave mode) that is
asserted to acknowledge an external device request for bus control
(i.e., assertion of a BR input). The DSP asserts the BG output signal
after a few T states to acknowledge receipt of the BR input. The DSP
releases control of the external bus at the earliest possible time
consistent with proper synchronization. At release, the DSP tri-
states PEREN, PS/DS, RD, WR, and R/W and deasserts the BB
output. When the BR and BB inputs are deasserted, the DSP regains
control of the bus and the BG output is deasserted.
Note:
If the master bit in the OMR is set, this signal is an input (Master
mode). In this mode the external bus master asserts BG to
acknowledge the BR signal generated by the DSP to request control
of the bus. The DSP begins processing external accesses on the
rising edge of the clock after the BB input generated by the other
bus master is sampled high. When the BG input is deasserted, the
DSP releases the bus as soon as the current transfer is complete.
Bus Busy—After reset, this signal is an input. An external master
asserts this input signal to indicate that it has control of the bus and
is performing a bus access. When the DSP acquires control of the
external bus and performs and external access, it asserts BB as an
output signal to the other bus master devices. The DSP deasserts BB
and it again becomes an input when the DSP releases bus control.
DSP56167/D, Rev. 1
BG may be asserted in the middle of an instruction that
requires more than one external bus cycle for execution, but
never during a read-modify-write instruction.
Signal Description
Signal/Pin Descriptions
Bus Control
1-9