SSM2163_15 Datasheet, PDF (15/16 Pages) Analog Devices – Digitally Controlled 8 3 2 Audio Mixer

SSM2163
Listing 1. Software for the 80C51-SSM2163 Serial Port Interface
; This subroutine loads an SSM2163 mixer channel with a 6-bit
; attenuator value, and turns the Left or Right mixer switch ON or OFF.
; The attenuator value is stored at location ATTEN_VALUE
; The mixer channel address is stored at location INPUT_ADDR
;
PORT1
DATA
90H
;SFR register for port 1
ATTEN_VALUE DATA
40H
;Attenuation level (0=0dB)
;ATTEN-VALUE: B7=0, B5–B0=Attenuation Value
INPUT_ADDR DATA
41H
;Mixer Channel Address
;INPUT_ADDR: B7=1, B4=L chnl, B3=R chnl, B2-B0=address
LOOPCOUNT DATA
42H
;Count loops for byte swap
OBSOLETE SHIFTREG
SENDBYTE
LD_2163:
SEND_VAL:
DATA
43H
;Shift reg. for byte swap
DATA
44H
;Destination reg. for byte swap
;
ORG
100H
;arbitrary starting address
CLR
SCON.7
;set serial
CLR
SCON.6
; data mode 0
CLR
SCON.5
;Clr SM2 for mode 0
CLR
SCON.1
;clr the transmit flag
CLR
PORT1.3
;Mute function off
SETB
PORT1.4
;WRITE and LOAD High
MOV
SHIFTREG,INPUT_ADDR
;Get mixer channel address
ACALL SEND_IT
; send to SSM2163
MOV
SHIFTREG,ATTEN_VALUE
;Get the attenuation level
ACALL SEND_IT
; send it to the SSM2163
RET
;Done
;
;Convert the byte to LSB-first format and send
; it to the SSM2163
SEND_IT:
MOV
LOOPCOUNT,#8
;Shift 8 bits
BYTESWAP: MOV
A,SHIFTREG
;Get source byte
RLC
A
;rotate MSB to carry
MOV
SHIFTREG,A
;Save new source byte
MOV
A,SENDBYTE
;get destination byte
RRC
A
;Move carry into MSB
MOV
SENDBYTE,A
;Save
DJNZ
LOOPCOUNT,BYTESWAP
;Done?
CLR
PORT1.4
;Set WRITE and LOAD low
MOV
SBUF,SENDBYTE
;Send the byte
SEND_WAIT: JNB
SCON.1,SEND_WAIT
;Wait until 8 bits are send
CLR
SCON.1
;Clear the serial flag
SETB
PORT1.4
;Set WRITE and LOAD high to latch
RET
; data into the SSM2163
END
The subroutine begins by setting appropriate bits in the Serial
Control register to configure the serial port for Mode 0
operation. Next the SSM2163’s Chip Select input is set low to
enable the SSM2163. The input channel address is obtained
from memory location INPUT_ADDR, adjusted to compensate
for the 80C51’s serial data format, and moved to the serial
buffer register. At this point, serial data transmission begins
automatically. When all 8 bits have been sent, the Transmit
Interrupt bit is set, and the Chip Select output is set high to
latch the channel address into the SSM2163. The subroutine
then sets Chip Select low again and proceeds to send the
attenuation value stored at location LEVEL_VALUE. When
the Chip Select input is returned high, the appropriate
SSM2163 input channel will be updated with the new
attenuation value and the subroutine ends.
The 80C51 sends data out of its shift register LSB first, while
the SSM2163 requires data MSB first. The subroutine therefore
includes a BYTESWAP subroutine to reformat the data. This
routine transfers the MSB-first byte at location SHIFTREG to
an LSB-first byte at location SENDBYTE. The routine rotates
the MSB of the first byte into the carry with a Rotate Left
Carry instruction, then rotates the carry into the MSB of the
second byte with a Rotate Right Carry instruction. After 8
loops, SENDBYTE contains the data in the proper format.
The BYTESWAP routine in Listing 1 is convenient because the
attenuator data can be calculated in normal LSB form. For
example, fading a channel on the SSM2163 is simply a matter
of repeatedly incrementing the LEVEL_VALUE location and
calling the SEND_VAL subroutine. (Remember, the 6-bit
REV. 0
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