6601 bank switch

Question

I am having difficulty getting a 6601 card to generate a variable duty cycle PWM under QNX6.3.0sp2. It works fine when I reset the TIO chip and program all the registers. Unfortunately that gives a glitch when changing duty cycles. I am trying the bank switch feature to eliminate the glitch. The sequence I am using is: 1) program all the registers for the inital PWM and enable software bank switching, 2) load registers A and B and trigger the bank switch. The problem I am having is the second step is giving a PWM with a mix of values from both steps. For example, step1 initial PWM of 100Hz 40% duty cycle sets A=80000 B=120000. I see the correct output. Step2, change to 100Hz 80% duty cycle (A=160000 B=40000) gives me 166.7Hz 66.7% which is A=80000 B=40000 (A from step1 and B from step2). Here is a code segment.
Step 1 (initial setup with ):
board->G01_Joint_Reset_Register.writeG0_Reset(1);
board->G0_Command_Register.writeG0_Write_Switch(0); // write to A only for initial time
board->G0_Command_Register.writeG0_Bank_Switch_Mode(1); // software bank switch
board->G0_Command_Register.writeG0_Bank_Switch_Enable(0); // disable bank switch, write to bank X
board->G0_Load_A_Registers.writeG0_Load_A(load_A); //A is the high count
board->G0_Load_B_Registers.writeG0_Load_B(load_B); //B is the low count
board->G0_Command_Register.writeG0_Load(1);
board->G0_Mode_Register.writeG0_Reload_Source_Switching(1); //reload from the other load register on each terminal count
board->G0_Mode_Register.writeG0_Loading_On_TC(1);
board->G0_Input_Select_Register.writeG0_Source_Select(30); //set source to internal timebase 3, the 20MHz internal clock (80MHz on 6602)
board->G0_Input_Select_Register.writeG0_Gate_Select(30); //set gate to disabled gating
board->G0_Mode_Register.writeG0_Gate_Polarity(1);
board->G0_Command_Register.writeG0_Synchronized_Gate(1);
board->G0_Mode_Register.writeG0_Trigger_Mode_For_Edge_Gate(3);
board->G0_Mode_Register.writeG0_Gating_Mode(1);
board->G0_Command_Register.writeG0_Up_Down(0); //set counting direction to down
board->IO_Pin_36_37_Configuration_Register.writeIO_Pin_36_Select(1); //set PFI line to output
board->G0_Mode_Register.writeG0_Output_Mode(10);
board->G0_Command_Register.writeG0_Write_Switch(1); // write to inactive register set
board->G0_Command_Register.writeG0_Arm(1); //arm counter
board->G0_Command_Register.writeG0_Bank_Switch_Enable(1); // enable bank switch
Step 2 (subsequent calls):
board->G0_Load_A_Registers.writeG0_Load_A(load_A);
board->G0_Load_B_Registers.writeG0_Load_B(load_B);
board->G0_Command_Register.writeG0_Bank_Switch_Start(1); // swap banks
Any ideas?
Doug

Answer 1

Hi Doug-
Semi-period measurements are supported on the NI 660x boards.  This feature is not documented in the 660x manual or an example, but setting it up should be very similar to the description given in the STC manual.  If you have any questions about performing this type of measurement on the 660x, please post back. 
Thanks-
Ed