Once installed on a SPLat controller, the SPice10218 appears as one analog input and 3 digital outputs. The following table shows the mappings for all the I/O on the board. Numbers in parenthesis are the numeric analog channel numbers used with fAnIn. You should use fAnIn to get the full benefit of 10-bit resolution.

The SPice10218 is a multiplexer. That means it has the ability to select any one of its 8 analog input lines and route that through to a single analog input on the main SPLat controller board, where it can be read by an analog input instruction, e.g. fAnIn. The channel to be read is selected by sending a binary coded channel number to 3 “channel select” outputs. The analog input channel used, and the 3 channel select outputs, vary between SPLat controller boards according to the table above.

Channel select patterns

The following table defines the bit patterns for the 3 channel select outputs and the corresponding input channel numbers.

You may recognize this as a simply binary count, which indeed it is. Note however that the the least significant channel select bit is in the most significant of the three outputs.

Initializing the SPice connector

Because the pins of the SPice connector, to which the SPice10218 is connected, can be configured for different functions (analog/digital, input/output), you need to have some code in your program that configures them to the correct settings for the SPice10218.

The following section of code should be run by your program just once, at the beginning, before your program attempts to do anything else with the SPice10218.

         ClrU
         setu         0,3         ;set spice connector pin 4 as analogue input
         setu         1,1         ;set spice connector pin 5 as digital output
         setu         2,1         ;set spice connector pin 6 as digital output
         setu         3,1         ;set spice connector pin 7 as digital output
         setu         4,0         ;set spice connector pin 8 as unchanged
         setu         5,0         ;set spice connector pin 9 as unchanged
         SpiceConfigU

Reading an analog value (example program)

Once the SPice connector has been initialized (which you would do early in your program using the code above), reading a channel requires setting the channel select outputs to the right pattern, allowing the analog voltage to settle, and then executing an analog input instruction.

The analog settling time must be taken into account. It cannot be ignored. The settling time constant is up about 0.5mS. It takes 7 time constants to settle to 10 bits. Hence the multiplexer requires at least 3.5mS to settle to 10 bits.

The following is a MultiTrack task that will automatically scan all 8 channels. To use it copy and paste the code into your program and edit the SP218_MUXStart and SP218_AnIn constant values to match your controller type. To start it up simply LaunchTask Scan218. To access a reading load X with the required channel number 0-7 and GoSub Get218Reading. The latest reading for the required channel will be returned in W as a normalized number 0-1.

* The following equates select the base address for the MUX select lines on the
* SPICE connector based on the board type:
*
* SL99, SL100                           SP218_MUXStart =  9, SP218_AnIn = 2
* MMi99, MMi200, MMi201, MMi202         SP218_MUXStart = 17, SP218_AnIn = 4
* MS12, MS120                           SP218_MUXStart = 13, SP218_AnIn = 2

SP218_MUXStart  equ     17      ;MMiXXX
SP218_AnIn      equ     4


Ch218           defBYTE
Readings218     defFLOAT        8       ;Result holding variables

;The scanner stores readings in an array of 8 floating point numbers.
;Because of the bit reversal that takes place on the 218 board, the 
;order of readings in memory will be scrambled. This gets sorted out
;by bit reversing the index used during readout, in Get218Reading.
Scan218:
                Recall          Ch218
                LoadX           7
                OutputM         SP218_MUXStart
                Pause           2	         ;Guarantee 10mS minimum settling delay.
                fAnIn           SP218_AnIn
                Recall          Ch218
                Push
                XtoI
                IasJ:fStore     Readings218
                IncX
                LoadX           7
                AndM
                Store           Ch218
                GoTo            Scan218

;Return the latest reading for the channel number in X
Get218Reading:
                GoSub           ReverseBits012
                XtoI
                IasJ:fRecallW   Readings218
                Return

ReverseBits012: ;Reverse bit order 0, 1, 2 in X         
RB_X1           defBYTE
RB_X2           defBYTE

RB_Y0           SetMem          RB_X2,0
                Store           RB_X1
                GoIfSF          0,RB_X1,RB_Y1
                SetS            2,RB_X2
RB_Y1           GoIfSF          1,RB_X1,RB_Y2
                SetS            1,RB_X2
RB_Y2           GoIfSF          2,RB_X1,RB_Y3
                SetS            0,RB_X2
RB_Y3           Recall          RB_X2
                Return