In Modbus RTU, you always read a byte. Naturally, in Modbus ASCII, you read characters, 8-bit characters, and each byte is a part of number represented as text:
http://en.wikipedia.org/wiki/Modbus#Frame_format[
^].
So, you either read individual byte or some number and extract an individual bit from the data read. All software developers know how to extract a bit, but… do you need help?
—SA