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ROMAC  H19MK101  -  H19 Video Terminal Board
This is perhaps one of the most unusual S-100 boards in the collection.  The board utilized only the power lines from the S-100 bus. No other pins were connected to the board.   In fact the board was often used outside the bus by simply connecting the required power lines to the solder points on the top left hand section of the board. It used less than 1 Amp on the +5 Volts line.

Romac H19 terminal Board

The ROMAC H19MK101 terminal provided the versatility needed for a truly efficient computer interface through its many built in features. These features included such things as Cursor Control/Reverse Video, simple graphics, Report Cursor Position, Downloadable Keyboard Handler Routines, Editing Functions and much more! It also provided a keyboard interface which could support special function keys and detachable keyboards easily.
For compatibility with available software, the ROMAC Terminal used the same command format as two popular terminals of the time; the Heath H-19 (or Zenith Z-19) and the Digital Equipment Corporation VT-52. This meant that any program written to use the special functions of either of these terminals  would  be  totally   compatible  with  the  ROMAC  Terminal.

This section will provide a brief circuit description of each of the major integrated circuit components of the ROMAC H19MK10l Terminal.

The Z80A is a 4MHZ version of the Z80 processor and was used to handle all IO control to and from the board. It had its own EPROM and used the 2K of the 4K of on-board RAM

Z80 DART or SIO/O Serial I/O Devices
These Z80 serial communication devices contain two serial I/O ports and their associated control logic. All common asynchronous serial protocols are supported. The SIO also supports many common bit or byte oriented synchronous protocols. Each channel of these devices has an 8 bit register for data to be transmitted and three registers in a FIFO arrangement for received data. In addition, each channel has eight control registers (ten for the SIO). These registers are accessed by first writing a byte which indicates which register is to be used. Register 2 of port B was used for the interrupt vector.

6845 CRT Controller
The 6845 is a device which coordinates all the functions necessary to control a CRT monitor device. Though video data doesn't actually pass through the device, it handles data transfer control, cursor positioning, and screen formatting tasks. It is in control of the display memory and character generation memory which provide the data to be displayed on the screen.  Although the 6845 is a complex device, it provides no internal logic for handling memory access arbitration or cursor generations external logic. These functions have to be provided by
the CRT Controller which has 19 internal registers which must be programmed with the operating parameters before the device can function. These parameters determine the timing characteristics of the CRT interface. The number of lines, number of characters per line, and location of the top of the page are derived from these characteristics.

The board had 2 K of static RAM for operations, 2K of display RAM, and 4 or 8K of EPROM.  The keyboard input could be RS-232 or TTL serial. Output was either composite video or separate H & V sync.  The display was 24X80 with a 25th line as an option. 

The manual for this board can be obtained here.


ROMAC S-100 Boards
H19 Video Board


This page was last modified on 10/25/2013