Motorola DSP96002 , MOTOROLA DSP96002 USERS MANUAL 2 - 17, , Figure 2-7. Bus Arbitration Scheme, 5.16.2 Bus Handshake Unit , , Figure 2-8. Bus Handshake Unit

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