hasp/plate01/command/ is for sending commands to the screen
hasp/plate01/state/ is for receiving updates from the screen
So the topic depends on the direction of the data flow.
Sending a message to topic
hasp/plate01/command/p1b2.val with payload
25 would be a valid command.
You can send a test MQTT message with a standalone program like MQTT Explorer or mosuito_pub.
Commands can be issued via the Serial commandline, telnet commandline or MQTT.
For MQTT, you can use either:
hasp/<nodename>/commandtopic with payload
hasp/<nodename>/command/<keyword>topic with payload
<parameter(s)>Leave the payload empty to get the current state without changing it.