Physical layer services & hardware protocols
Just a quick answer:

Hardware protocols are at the lowest level of the Open System Interconnection (OSI) model and are usually a mix of


hardware specifications (cables, connectors,  signals, ...)
how data is exchanged between the hardware devices (start of communication, end of communication, data exchange, flow of control, timings, error handling, ...)


Typical examples of hardware protocols are: serial port RS-232, Parallel port IEEE 1284, USB , Ethernet, bus protocols, ...

Physical layer services are those functions used to correctly implement and manage the communication between devices at the physical layer: e.g. open a port, convert bits to timed signals, change the bit-rate, close a port, send data, multiplexing, flush data,  ...