MC3310 Datasheet, PDF (72/83 Pages) List of Unclassifed Manufacturers – Motion Processor

7.6 16-bit Serial DAC Interface
The following schematic shows an interface circuit between the MC3310 and a dual 16-bit serial
DAC.
Comments on Schematic
The 16 data bits from the CP chip are latched in the two 74H165 shift registers when the CP writes
to address 400x hex, and the address bits A1 and A2 are latched in the 2 DLAT latches and decoded
by the 138 CPU cycle. The fed-back and-or gate latches, the decoded WRF, and the next clock will
clear the 1^st sequencer flop DFF3. This will disable the WRF latch and the second clock will clear
the second DFF3 flop, forcing DACWRN low, and setting the first flop since WRF will have gone
high. DACWRN low will clear the 74109, SHFTCNTN. The 4 bit counter, 74161, is also parallel
loaded to 0, and the counter is enabled by ENP going high. The counter will not start counting nor
the shift register start shifting until the clock after the DACWRN flop sets since the load overrides
the count enable. When the DACWR flop is set the shift register will start shifting and the counter
will count the shifts. After 15 shifts CNT15 from the counter will go high and the next clock will set
the DACLAT flop and set the SHFTCNTN flop. This will stop the shift after 16 shifts and assert
L1 through L4 depending on the address stored in the latch. The 16th clock also was counted
causing the counter to roll over to 0 and CNT15 to go low. The next clock will therefore clear the
DACLAT flop causing the DAC latch signal L1 through L4 to terminate and the 16 bits of data to be
latched in the addressed DAC. The control logic is now back in its original state waiting for the next
write to the DACs by the CP. SERCK is a 10MHz clock, the 20MHz CP clock divided by 2, since
the AD1866 DACs will not run at 20MHz.
MC3310 Technical Specifications
72