Loading Registers from a Host CPU
The X14:0 expansion data inputs on a single or master device
are connected to the host bus to provide address and data for the
internal registers. In a multiple device system the remaining
devices receive addresses and data which have been passed
through the expansion connection between earlier devices in the
cascade chain. Each device needs an individual chip enable
(
CE
) plus a global data strobe (DS), a read/ not write (
R/W
) line,
and
PROG
signal from the host.
Registers are individually addressed and can be loaded in any
sequence once the global
PROG
signal has been produced by the
host. The latter would normally be produced from an address decoder
encompassing all the necessary device addresses.
If a self-timed system is to be implemented, a timing strobe
must be passed down the expansion chain through
the
PC0/PC1
connections. The
PC0
output from the final device
is used as a host
REPLY
signal, and indicates that the last
device has received data after the propagation delay of previous
devices. The timing strobe is produced in the Master device from
the host data strobe, and will appear on the
PC0
output. This
feature allows the user to cascade any number of devices without
having to know the propagation delay through each device. The
timing information for this mode of operation is given in Fig. 10.
The host can also read the data contained in the internal registers.
The required device is selected using chip enable with the
R/W
line
high, indicating a read operation. Single device systems output the
data read on X7:0, but in multiple device systems data is read from
the D7:0 outputs on the final device in the chain. These must be
connected back to the host data bus through tristate drivers, whose
tristate control must be generated externally (see Figs. 14 and 15).
When earlier devices in the chain are addressed, the register
contents are transferred through the expansion connections down to
the final device. In the self timed configuration the data will be valid
when
REPLY
is taken low by
PC1
, as shown in Fig. 10.
If
REPLY
is not to be used, the
PC0/PC1
connections are
not necessary, and the host data strobe for a write operation must
be wide enough to allow for the worst case propagation delay
through all the devices (t
DEL
). If the data or address from the host
does not meet the set up time given in Fig. 8, the width of the data
strobe can be simply extended to compensate for the additional
delay. When reading data the access time required is
t
ACC
t
DEL
(N 1), using the maximum times given in the Host
Mode Switching Characteristics.
Host control lines
X7:0
8-bit data bus. In a Single device system this bus is
bidirectional; in other configurations it is an input.
Only a Single or Master device is connected directly
to the host. Other devices receive data from the
output of the previous device in the chain.
X14:8
7-bit address bus which is used to identify one of the
73 internal registers. Connected in the same man-
ner as X7:0.
X15 must be open circuit on the Master device
An input from the previous
PC1
output in a multiple
device chain. Not needed on a Single device or if the
self timed feature is not used.
Reply to the host from a Single device or from the
last device in a cascade chain. It indicates that the
write strobe can be terminated. Connected to
PC0
input of the next device at intermediate points in the
chain if the self timed feature is used.
R/W
Read/Not Write line from the host CPU which is
connected to all devices in the system.
An active low enable which is normally produced
from a global address decode for the particular
device. This must encompass all internal register
addresses.
An active low host data strobe which is connected to
all devices in the system.
An active low global signal, produced by the host,
which is connected to all devices in the system.
Together with a unique chip enable for every device,
it allows the internal registers to be updated or
examined by the host
PROG
and
CE
should be tied
together in a Single device system.
CE
DS
PROG
Loading Registers from an EPROM
In the EPROM mode, one device has to assume the role of
a host computer. If more than one device is present, this must be
the first component in the chain, which must have its
MASTER
pin tied low.
The Master device contains internal address counters which
allow the registers in up to 16 cascaded PDSP16488As to be
specified. It also generates the
PROG
signal and a data strobe
on the pins which were previously inputs. These outputs must be
connected to the other devices in the system, which still use them
as inputs. The
R/W
input should be tied low on all devices.
The width of the data strobe is determined by the feedback
connection from the
PC1
output on the last device to the
PC0
input
on the Master. The
PC0/PC1
connections must be made be-
tween devices in a multiple device system; in a single device
system the connection is made internally.
The available EPROM access time is determined by an
internal oscillator and does not require the pixel clock to be
present during the programming sequence. Any pixel clock re-
synchronization in a real time system will thus not affect the
coefficient load operation. The relevant EPROM timing informa-
tion is shown in Fig. 11.
The load procedure will commence after
RES
has gone from
low to high, and will be indicated by the
PROG
output going
low. The data from 73 EPROM locations will be loaded into the
internal registers using addresses corresponding to those in
Table 5. Within a particular page of 128 EPROM locations, the
first nine locations supply control register information, and the
top 64 supply coefficients. The middle 55 locations are not
used. If the window size is 8 4, the top 32 locations will also
contain redundant data, and if the size is 4 4 the top 48 will
be redundant.
In a multiple device system the load sequence will be re-
peated for every device, and four additional address bits will be
generated on the CS3:0 pins. These address bits provide the
EPROM with a page address, with one page allocated to each
device in the system. Within each page only 73 locations provide
data for a convolver, the remainder are redundant as in the single
device system. The CS3:0 outputs must also be decoded in order
to provide individual chip enables for each device. These can
readily be derived by using an AS138 TTL decoder. Bits in an
internal control register determine the number of times that the
sequence is repeated.
If changes to the convolver operation are to be made after
power-on, activating the
CE
input on the Master or Single
device will instigate the load procedure. Additional EPROM
address bits supplied from the system will allow different filter
coefficients to be used.
X15
PC0
PC1
13
MITEL [ MITEL NETWORKS CORPORATION ]
