H89 system disk creation

This page last updated June 15 2020. Edited by Herb Johnson, (c) Herb Johnson, except for content written by Lee Hart.

Introduction by Lee Hart

There have been discussions of ways to bring up an H8 or H89 when you don't have any bootable disks. Most solutions involve transferring programs to the H8 or H89 from a desktop PC. Those programs will load in other programs and files, which will format and write a system diskette (HDOS or CP/M). Most of these are are "special case" solutions that work for some situations, and not others.

I said, "You know, the H89 CPU board has a standard RS-232 port, and its built-in monitor can already load programs into memory and execute them. Why not re-connect it to your PC serial port, use your PC as its "console", and use the H89's monitor to download and run programs to create a new bootable CP/M disk?"

H89 CPU serial transfer cabling

Responses were: "I didn't think of that!" and "I didn't know the pinouts of the stock Heath serial cables were correct to connect the CPU board to an RS-232 port."

Since the H-89 3-port board's serial cable's pinouts are identical to the CPU-TLB (terminal logic board) cable, you already have a cable from that board. It will have the 15-pin CPU header on one end, and a standard RS-232 DB-25 on the other end. This cable's header end can be moved from the 3-port board to the CPU board.

Which cable, the DTE or DCE?

It depends on what you need to plug it into. The pinouts and wires are the same on both of them. The only difference is the gender of the DB-25 on the DB-25 end (female is DCE, male is DTE).

Note the direction! Many serial problems are caused by mixing up the inputs and outputs. "TXD" pin 3 on the H89 CPU board is its serial *input* (i.e. it receives data from the external world's TXD output). In the chart below, the arrows show the flow of data.

connector		Heath 134-1073	134-1070	home-made
P513 on			"DCE" cable	"DTE" cable	cable for 9-pin
H89 CPU			female female	female male	PC serial port
board	direction	15-pin DB-25	15-pin DB-25	DB-25 to DB-9
------	 --------	-------------	-------------	-------------
1 GND	 ========	black ----1,7	black ---- 1	1 === GND === 5
3 TXD	 <-------	brown <--- 2	brown <--- 2	2 <-- TXD <-- 3
5 RXD	 ------->	red -----> 3	red -----> 3	3 --> RXD --> 2
7 RTS	 <-------	orange <-- 4	orange <-- 4	4 <-- RTS <-- 7
9 CTS	 ------->	yellow --> 5	yellow --> 5	5 --> CTS --> 8
11 DSR	 ------->	green ---> 6	green ---> 6	6 --> DSR --> 6
13 GND	 ========	blue ----- 7	blue ----- 7
14 DTR	 <-------	violet <- 20	violet <- 20	20<-- DTR <-- 4
15 RLSD	 ------->	gray ----> 8	gray ----> 8	8 --> RI  --> 9

The original IBM PC had a male DB-25 "DTE" serial connector (TX output on pin 2 etc.) If you're connecting to an old PC clone's serial 25-pin male DB-25, use the Heath 134-1070 cable (with a straight-through male-female cable to extend its length).

Later PC-compatibles had a male 9-pin DB-9 serial connector. The cable you need to connect it is shown in the last column above.

Lee Hart, June 2020
edits by Herb Johnson with permission

operation of the H89 ROM monitor

Here's some instructions about operating the Heath H89 ROM monitors. They vary a little from revision to revision; some H89's may have non-Heath monitor. See if these commands will work.

Where do I get H89 disk images?

SEBHC has established a repository for H8 and H89 diskettes images.

Dave Dunfield's classiccmp archive of imagedisk tools There's also tools for the Heath H8, including a HDOS 1.6 disk image for the H8 and H89.

By established convention, Heath H8 and H89 *hard sectored* diskettes are imaged as a single file in what's called "H8D" format. That is simply a sequential copy of each sector of the given diskette, from track 0 outward. I believe the tracks for double-sided diskettes are imaged (and accessed by their DOSes) as bottom-track then bottom-track pairs; the bottom being the single-sided side. H8 and H89 *soft sectored* diskettes are likely in "IMG" or "IMD" formats, refer to Dunfield IMAGEDSK for details but those are also sequential sector formats. Whatever the details, these are the established imaged-disk formats for the H8 and H89.