
Memory Interface Signals
9-4
Table 9–1.Global Memory Interface Signals
Signal
Type
§
Description
Value After
Reset
Idle
Status
||
AE
I
Address bus enable signal for global-memory interface.
When high (set to 1), places address lines A30–0 in the high-
impedance state.
N.A.
#
ignored
CE(0,1)
I
Control signal enable for R/Wx, STRBx, and PAGEx signals.
When high (set to 1), it places the corresponding R/Wx,
STRBx, and PAGEx signals in high-impedance state (x = 0
for CE0 and x = 1 for CE1).
N.A.
ignored
DE
I
Data bus enable signal for global memory interface. When
high (set to 1), places data lines D31–0 in the high-imped-
ance state. Reads can still occur but writes cannot.
N.A.
ignored
LOCK
O
Lock signal for global bus interface. Indicates whether an
interlocked access is underway (0 = access underway;
1 = access not underway). LOCK is changed onlyby the in-
terlocked instructions.
1
1
PAGE(0,1)
O/Z
Memory-page enable signal for STRB(0,1) accesses
0
0
RDY(0,1)
I
Indicates external memory is ready to be accessed
N.A.
ignored
R/W(0,1)
O/Z
Specifies memory read (active high) or write (active low) mode
1
1
STAT(3–0)
O
Four lines that define the status or function of the memory
port as shown in Table 9–2 (next page).
all 1s
all 1s
STRB(0,1)
O/Z
Interface access strobe
1
1
A(30–0)
O/Z
Address bus. The address lines are always driven. They keep
the address of the last access.
Hi–Z
address
of last
access
D(31–0)
I/O/Z
Data bus. These signals go to high impedance between write
accesses.
Hi–Z
Hi–Z
The numbers in parentheses mean that either a 0 (zero) or a 1 can follow the prefix shown to the left of the parenthesis. A zero
indicates STRB0 control signals (shown in Figure 9–1), and a one indicates STRB1 control signals.
STAT(3–0) and LOCK 
cannot
 be controlled by an external control signal.
§O=output; I=input; Z=high-impedance state.
This signal can be used in a shared bus configuration to hold the ’C4x off the shared bus while another ’C4x accesses the shared
memory and peripherals.
#N.A. means not affected.
||Idle status = no external memory access
Table 9–2 shows how pins STAT3 to STAT0 define the current status of the
global-memory port. For bus accesses, these signals provide information
about the access that is about to begin. The code for a SIGI instruction read
is useful for distinguishing between a SIGI read and a LDII or LDFI read.