Initialization; Operation; Read Operation; Write Operation - Intel iSBX 350 PARALLEL MULTIMODULE BOARD Hardware Reference Manual

Programming Information
through 6) defines the operating mode for Port A
(address XO or X4) and the upper four bits of Port C
(address X2 or X6). Group B (control word bits XO
through
X2)
defines the operating mode for Port B
(address
Xl
or
X5)
and the lower four bits of Port C
(address
X2
or
X6).
Bit
7
of the control word reflects
the mode set flag.
3-5. INITIALIZATION
To initialize the PPI, write a control word to port
address X3 (or X7). Refer to figure 3-1 and table 3-2
and assume that the control word is 92 (hexadecimal).
This initializes the PPI as follows:
a. Mode Set Flag active
b. Port A
(XO
or
X4)
set to Mode 0 Input
c. Port C
(X2
or
X6)
upper set to Mode 0 Output
d. Port B
(Xl
or
X5)
set to Mode 0 Input
e. Port C (X2 or X6) lower set to Mode 0 Output
3-6. OPERATION
After the PPI has been initialized, the operation is
simply performing a READ or a WRITE to the
appropriate port.
iSBX 350
3-7. READ OPERATION. A typical read subrou-
tine for Port A is given in table
3-3.
3-8. WRITE OPERATION. A typical write sub-
routine for Port C is given in table 3-4. As shown in
figure 3-2, any of the Port C bits can be selectively
set or cleared by writing a control word to address
X3.
CONTROL WORO
BIT SET/RESET
1 = SET
0= RESET
BIT SET/RESET
L - - - - - - - - - -..
I ENABLE
0= ACTIVE
Figure 3-2. PPI Port C Bit Set/Reset
Control Word Format
Table 3-2. Typical PPI Initialization Subroutine
3-2
;INT PAR INITIALIZES PARALLEL PORTS.
;USES-A: DESTROYS-A.
INT PAR: MVI
OUT
RET
END
A,92H
BASAD
+
3
;MODE WORD TO PPI PORT A & BIN, C OUT
;BASE ADDRESS
+
3
Table 3-3. Typical PPI Port READ Subroutine
;AREAD READS A BYTE FROM PORT A INTO REG A.
;USES-A; DESTROYS-A.
AREAD:
IN
RET
END
BASAD :INPUT BYTE (BASE ADDRESS)
Table 3-4. Typical PPI Port WRITE Subroutine
;COUT OUTPUTS A BYTE FROM REG A TO PORT C.
;USES-A; DESTROYS-NOTHING.
COUT: OUT
RET
END
BASAD + 2 ;OUTPUT BYTE (BASE ADDRESS
+
2)