Introduction
C513AO
User’s Manual
1-10
05.99
PSEN
29
32
26
O
Program Store Enable
This is a control signal that enables output of the external
program memory to the bus during external fetch
operations. It is activated every six oscillator periods
except during external data memory accesses. It remains
high during internal program execution.
This pin should not be driven during reset operation.
ALE
30
33
27
O
Address Latch Enable
This output is used for latching the low-byte of the address
into external memory during normal operation. It is
activated every six oscillator periods except during an
external data memory access. When instructions are
executed from internal program memory (EA = 1) the ALE
generation can be disabled by bit EALE in SFR SYSCON.
This pin should not be driven during reset operation.
EA
31
35
29
I
External Access Enable
When held at high level, instructions are fetched from the
internal program memory when the PC is less than 4000
H
.
When held a t low level, the C5 13AO f etches all
instructions from external program memory.
This pin should not be driven during reset operation.
Note: For the C513AO-L this pin must be tied low.
P0.0-
P0.7
32-39 43-36
37-30
I/O Port 0
Port 0 is an 8-bit open-drain bidirectional I/O port. Port 0
pins that have “1”s written to them float, and in that state
can be used as high-impendance inputs. Port 0 is also the
multiplexed low-order address and data bus during
accesses to external program or data memory. In this
application, it uses strong internal pull-up transistors when
issuing “1”s. External pull-up resistors are required during
program verification.
*)
I = Input
O = Output
Table 1-1
Pin Definitions and Functions (cont’d)
Symbol Pin Number
I/O
*)
Function
P-DIP-40
P-LCC-
4
4
P-MQ
F
P-44