W78C438C
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Notes:
1. The instructions used to access these nonstandard registers may cause assembling errors with respect to the 2500 A. D.
assembler, but these errors can be ignored by adding directive ".RAMCHK OFF" ahead these instructions.
2. In the newly added SFR of W78C438C, only XICON register is bit-addressable.
Power Reduction Function
The W78C438C supports power reduction just as the W78C32 does. The following table shows the
status of the external pins during the idle and power-down modes.
FUNCTION
ALE, PSEN
P0
−
P3, P8
DP4
AP5, AP6
AP7
Idle
1 1
Port Data
Floating
Address
Note
Power Down
0 0
Port Data
Floating
Address
Note
Note: AP7 is either 0 or a value decoded by AP6<7:6>, depending on the value of EPMA.7.
Programming Difference
The W78C438C is programmed in the same way as the W78C32, except that the external data RAM
is accessed by a "MOVX @Ri" instruction. To support address paging, there is an additional 8-bit SFR
"HB" (high byte), which is a nonstandard register, at address 0A1H. During execution of the "MOVX
@Ri" instruction, the contents of HB are output to AP6. The page address is modified by loading the
HB register with a new value before execution of the "MOVX @Ri" instruction. To read/write the HB
register, one can use the "MOV direct" instruction or "read-modify-write" instructions. The HB register
does not support bit-addressable instructions.
[Example].
MOV
R1, #0H
; R1 = 0.
MOV
0A1H, #0FFH
; HB contents FFH.
MOVX
A, @R1
; Read the contents of external RAM location FF00H into
; Accumulator.
MOV
0A1H, #12H
; HB contents 12H.
MOVX
@R1, A
; Copies the contents of Accumulator into external RAM
; location 1200H.
ABSOLUTE MAXIMUM RATINGS
PARAMETER
SYMBOL
MIN.
MAX.
UNIT
DC Power Supply
V
DD
−
V
SS
-0.3
+7.0
V
Input Voltage
V
IN
V
SS
-0.3
V
DD
+0.3
V
Operating Temperature
T
OPR
0
70
°
C
Storage Temperature
T
STG
-55
+150
°
C
Note: Exposure to conditions beyond those listed under Absolute Maximum Ratings may adversely affect the life and reliability of the
device.
