B&B Electronics 485SDD16 manual Software, Programming Techniques, Digital I/O Mask Values

Chapter 5 - Software

This chapter will be divided into two sections. The first section covers programming techniques for constructing a command string, receiving data and manipulating data in QuickBASIC. The second section discusses how to install and run the demonstration program on an IBM PC or compatible.

Programming Techniques

This section shows steps and examples of programming the 485SDD16 in QuickBasic. If you are programming in another language, this section can be helpful as a guideline for programming the 485SDD16.

Read I/O Lines Command

The Read I/O Lines command returns two data bytes that represents the states of the module's I/O lines. Refer to this

command in Chapter 3 for more information. Step 1 - Constructing the command string:

Cmnd$ = "!" + CHR$(Maddr) + "RD"

Where Maddr is the address of the module that is to return its I/O states.

Step 2 - Transmitting the command string:

PRINT #1, Cmnd$; Step 3 - Receiving the data:

MSIO$ = INPUT$(1,#1)

LSIO$ = INPUT$(1,#1)

Step 4 - Manipulating the data:

MSIO = ASC(MSIO$)

LSIO = ASC(LSIO$)

Step 5 - Determining an I/O's status:

MSstatus = MSIO AND mask

LSstatus = LSIO AND mask

By "ANDing" the value of MSIO or LSIO with the appropriate mask of an I/O line, the status of the I/O line can be determined. If the status is equal to zero the I/O line is LOW. If the status is not equal to zero the I/O line is HIGH. Table 5.1 shows the mask values for each I/O line.

Step 6 - Repeat Step 5 until the status of each I/O line has been determined.

485SDD16-1005 Manual	21
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Example 5.1 - Determining the status of I/O lines #2 & #10 of module #5.

Maddr = 5 mask = &H4

Cmnd$ = "!" + CHR$(Maddr) + "RD" PRINT #1, Cmnd$;

MSIO$ = INPUT$(1,#1)

LSIO$ = INPUT$(1,#1)

MSIO = ASC(MSIO$)

LSIO = ASC(LSIO$) MSstatus = MSIO AND mask LSstatus = LSIO AND mask

If LSstatus equals zero then I/O line #2 is LOW. If LSstatus is not equal to zero then I/O line #2 is HIGH. If MSstatus equals zero then I/O line #10 is LOW. If MSstatus is not equal to zero then I/O line #10 is HIGH.

Table 5.1 - Digital I/O Mask Values

I/O Line #	Mask Values
	Hexadecimal	Decimal
0 & 8	1H	1
1 & 9	2H	2
2 & 10	4H	4
3 & 11	8H	8
4 & 12	10H	16
5 & 13	20H	32
6 & 14	40H	64
7 & 15	80H	128

Read Configuration Command

The Read Configuration command reads the module's I/O definitions, Power-up states, Address, and Turn-around delay respectively. Refer to this command in Chapter 3 for more information.

Step 1 - Constructing the command string:

Cmnd$ = "!" + CHR$(Maddr) + "RC"

Where Maddr is the address of the module that is to return its configuration.

Step 2 - Transmitting the command string:

PRINT #1, Cmnd$;

22485SDD16-1005 Manual

B&B Electronics -- 707 Dayton Road -- Ottawa, IL 61350

PH (815) 433-5100 -- FAX (815) 433-5104