GP2021 Datasheet, PDF (21/62 Pages) Mitel Networks Corporation – GPS 12 channel Correlator Advance Information

V_DD
V_DD
OR
V_SS
V_DD
OR
V_SS
NARMSYS
GP2021
WRPROG
NINTELMOT
NCS
ALE_IP
WREN
READ
MICRO_CLK
D<15:0>
A<9:2>
GP2021
Address
Decode
Logic
High Address Lines
MICROPROCESSOR
NOTE: NRESET_OP, ACCUM_INT, and MEAS_INT are not shown
Fig.21 Standard Interface Mode
Control Signals
In Standard Interface Mode (NARMSYS held high), the
microprocessor interface of the GP2021 consists of two mode
control pins, (NINTELMOT and WRPROG), and the control
signals themselves, (ALE_IP, NCS, WREN and READ; the
exact function of which is dependent upon the interface style
selected).
Motorola Style Interface
(NINTELMOT = ’1’, WRPROG = ’X’)
The WRPROG mode control pin is not used in Motorola
Interface mode and should be tied High or Low. The ALE_IP
(Address Latch Enable input) pin is used to transparently latch
the address lines A<9:2> to the GP2021. If these address lines
are already latched externally, this pin may be tied High. Note
that the internal ALE signal is inhibited during a read or write
strobe so the address lines may be changed once the read or
write strobe has become active. The WREN pin acts as a
WRITE/READ ENABLE strobe (active High) with the READ
pin selecting either a READ strobe (READ = ’1’) or a WRITE
strobe (READ = ’0’). In a similar way to the addresses being
latched during a read or write strobe, the READ signal is also
latched during a data strobe and may be changed towards the
end of the cycle.
The NCS pin is an active low chip select used to gate out
the internal read and write strobes. In Standard Interface
Mode, the GP2021 can best be visualised in terms of 3 signals,
ALE_INT, WRSTROBE_INT and RDSTROBE_INT, the
internal ALE, write strobe and read strobe signals. In Motorola
Style Interface Mode these signals are derived as follows:
ALE_INT=ALE_IP. (WRSTROBE_INT + RDSTROBE _INT)
WRSTROBE_INT = NCS.WREN.READ
RDSTROBE_INT = NCS.WREN.READ
WREN the active low write strobe ( WREN= WRSTROBE).
NCS is the active low chip select used to gate out internal data
strobes.
ALE_INT=ALE_IP
WRSTROBE_INT = NCS.WREN
RDSTROBE_INT = NCS.READ
INTEL 486 Style Interface
(NINTELMOT = ’0’, WRPROG=’1’)
The Intel 486 Style Interface is similar to the 80186 style
interface, with similar separate read and write strobes. Some
of the later Intel microprocessors (notably the i486) have a
very small delay between the rising edge of ALE and the falling
edge of the read or write strobes. Due to the pre-charged
nature of the data–out bus of the Correlator, the address
inputs must remain stable throughout the read strobe, and the
small delay from ALE to read strobe would produce insufficient
address setup times for correct operation. The 486 style
interface mode removes this problem by gating both the read
and write strobes such that they are inhibited until the falling
edge of ALE_IP. The ALE_IP pin must not be tied High in 486
Style Interface mode.
ALE_INT= ALE_IP
WRSTROBE_INT = NCS. WREN. ALE_IP
RDSTROBE_INT = NCS. READ. ALE_IP
Reset
The NRESET_IP pin allows the GP2021 to be provided
with an external system reset.
For further information refer to System Reset in Standard
Interface Mode.
INTEL 80186 Style Interface
( NINTELMOT = ’0’, WRPROG = ’0’)
In the 80186 Style Interface mode the ALE_IP acts as an
Address Latch Enable input ( as in Motorola mode), used to
transparently latch the address lines A<9:2> to the GP2021.
Similar to Motorola mode, if the addresses are latched
externally this pin may be tied High. Whereas Motorola mode
used a single strobe input and a Read/Write level to denote
read and write strobes, both INTEL modes use a pair of strobe
inputs, one for reads, and one for writes. In this mode, READ
acts as the active low read strobe ( READ =RDSTROBE) and
Register Addressing
As shown in the GP2021 Register Map, register
addresses differ from those in ARM System Mode. In
particular in Standard Interface Mode the GP2021 address
bus interface is via A<9:2>, with NCS acting as its chip select
input. The address pins A0, A1 in ARM System Mode now
become the NRESET_IP and ALE_IP inputs. Hence,
depending upon the system configuration employed, A<9:2>
of the GP2021 could be connected to the microprocessor
address pins A<7:0>.
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