California Computer Systems - 2810  Z80 CPU Board
Being a late arrival on the S-100 bus scene this board had some nice features others lacked.

The CPU could be run at 2 or 4 MHz via the switch at the top of the board. Three diagnostic LEDs were provided on the 2810. One indicated that the ROM was enabled and selected. The second indicated that the CPU was executing a software Halt instruction and was waiting for an interrupt. The third LED indicated that CPU had been programmed to accept interrupts.
 
Since the Z80 would remain halted while executing a Halt instruction (until the system is reset or the CPU receives an interrupt), the last two LEDs could be used in combination to detect software problems of the CPU receiving a Halt instruction before it receives an Interrupt Enable instruction. Very useful! 
 
The board contained an on-board, asynchronous serial I/O port (using an 8250) which allowed you to interface to the CPU any serial I/O device which conforms to a major subset of the RS-232-C standards for asynchronous serial communications. You had several options in using this port. If you were using the monitor firmware as is, you were provided with driver routines for the port. These routines intend that the port be used to interface the CPU to some type of console device, preferably a CRT. For flexibility, the baud rate can be set through console control. Or you could, of course, use your own driver software for the port.  The port's address was jumper-selectable. You could also disable the serial port with an on-board jumper.
 
There was the usual power on jump to the on-board EPRO routine of course.  CCS used the boot address of F000H. The onboard monitor looks to me to be very like the TDL Zapple monitor. The Z80 refresh signal was put out on pin 66.
 
The manual for this board can be obtained here.