Welcome to the forum.
Use an output enable to gate the trigger pulse. Because you do not need (hopefully) to read all sensors in parallel you could use a different approach: Tie all echos together and use 8 triggers.
I "believe" the pin can be switched between I and O modes in hardware or in software.
#define Pin_DM_DIG_HIZ (0x01u) // High Impedance Digital.
#define Pin_DM_STRONG (0x06u) // Strong Drive.
PIN_SetDriveMode(Pin_DM_STRONG); //digital output
PIN_SetDriveMode(Pin_DM_DIG_HIZ); //digital input
Else you can try to declare pin for both input and output with "output enable" and try to get it work this way (untested).
Thanks for the above suggestions.
Regarding tying the echo pins together, the problem there is that they aren't open collector outputs. The echo pin is pulling 23 ma. I tried tying just two sensors together. I could see a pulse but the output voltage was less than a volt.
As for setting the pin direction, that really isn't the problem. The problem is the output drive of the echo pin vs the Psoc4 pin. On the Psoc4, electrically, I can't tie echo and trigger pins together and still get the Psoc4 to drive the pulse. So, the same problem exists even with the output enable on the pin. If I enable the Psoc4 pin output while its tied to echo pin, the echo pin will pull it down.
As an experiment, I tried tying the trigger outputs together, just to reversing the idea by Bob, but that causes all the sensors to emit their 40kHz signal at the same time which causes interference.
I've been searching to understand the drive output for the Arduino to understand how that's working. At this point, I still like the idea of tying all the echos pins together, but it looks like I'll to electrically convert them before I can connect to the Psoc. I did find a schematic for the HCSR04 and it shows the both echo and trigger pins being pulled up via a 10k resister into a OTP. Maybe it will help.
hcsr04schematic.png 98.5 K