Motorola DSP96002 - Manual (Page 20)

MOTOROLA DSP96002 USER’S MANUAL 2 - 17
An implementation of a bus arbitration scheme may hold
—
B
–
G asserted, for example, to the current bus
owner if none of the other devices are requesting the bus. As a consequence, the current bus master may
keep
—
B
–
A asserted after ceasing bus activity, regardless of whether
—
B
–
R is asserted or deasserted.
This situation is called "bus parking" and allows the current bus master to use the bus repeatedly without
re-arbitration until some other device requests the bus.
5.16.2 Bus Handshake Unit
The bus handshake unit in the DSP96002 is implemented within a finite state machine. It consists of two
external outputs (
—
B
–
R,
—
B
–
A), two external inputs (
—
B
–
G,
—
B
–
B) and three internal inputs
(ext_acc_req, end_of_sequence, RH) (see Figure 2-8). The ext_acc_req signal is asserted when one or
more requests for external bus access are pending, and remains asserted as long as the transfers are
being executed. The end_of_sequence signal is asserted at the last bus cycle of the current sequence.
DSP96002
Figure 2-7. Bus Arbitration Scheme
—
B
–
—
B
–
—
B
–
—
B
–
L
—
B
–
—
B
–
—
B
–
—
B
–
—
B
–
L
—
B
–
DSP96002
ARBITRATION
LOGIC
Figure 2-8. Bus Handshake Unit
—
B
–
R
—
B
–
A
ext_acc_req
end_of_sequence
Request Hold (RH)
—
B
–
BUS
HANDSHAKE
UNIT
—
B
–
B
V
cc