I recently did something similar that used Darrel's Instant Interrupt routines and 3 LED displays.

Displays were controlled in a tight loop, staying on for 6 msec each digit.

Data are comming in packets of 3 bytes but on the RS-485 bus are 1 tx device and 3 rx, so really the data are 9 bytes at random times.

Each display gets its own data rejecting the others. Interrupts work great and there is no loss of LED scanning.

Sorry that cannot post the whole code but if you have troubles please post you schematic and may be I can help you more.

Please note that is a must to use a PIC with hardware USART.

Ioannis