Siemens Simatic S5 PG685

The machine used to design programs for PLC controllers using Siemes Step5 software and load them into industrial machines. It is a portable PC which was originally a CP/M machine, so it is more CP/M machine than PC. Because the S5 line of PLC controllers was manufactured since early 1980s, their reliable design didn't changed much and Siemens manufactured these computers until early 1990s using the same design with CRT display. The only thing that changed is mainboard, in this unit it contains a 80286 CPU with about 1MB of RAM, but I doubt that 286 instructions are used by DOS 2.11 or CP/M-86. The machine has a small CRT display, set of programmable keys, a quad-density 5.25" floppy disk drive and 20MB ST225 MFM hard drive.
It is not fully compatible with IBM PC, it's more a CP/M-86 machine, so it is difficult to run any DOS software on it. It can run a special, customized version of MS-DOS 2.11 booted from a 720kB 5.25" quad-density disk or hard drive.
PG685 has a special socket for programming an EPROM module which contains program for controller. The specialized expansion board contains a full EPROM programmer electronics for it.
RTC is kept using 2 AA batteries located in the rear of computer in a fuse-like screw sockets.

Manufacturer	Siemens
Origin	Germany
Year of unit	1989
Year of introduction	1985?
Type	Portable, PC-incompatible
CPU	Intel 80286
RAM	1024kB
Floppy Disk	1x5.25", 720kB (QD)
Hard Disk	20MB MFM
Other media	None
Graphics and display:	?Text-mode?, built-in CRT (monochrome, white)
Sound:	PC Speaker
Keyboard and pointing device:	Full-stroke keyboard with keys specialized for programming a control process.
OS:	MS-DOS 2.11, customized version on 720kB 5.25" disk Probably CP/M-86.
		Power supply:
		Built-in switching power supply
I/O:	- Serial port - Parallel port - EPROM Module connector - Monitor output - Small DB9 port - AG S5 (programming) port - "SINEC H1" port (whatever it is)






Possible upgrades:	None known, possible by adding expansion boards
Additional peripherals:

Source of my device is not known, but it was salvaged from recycling plant. it is interesting that this computer contained 2 AA batteries made around early 1990s (best before 1993) in West Germany, which were still giving about 1.33V each. Another example of "German quality".
Update: Batteries gave up in 2019, after more than 3 years of powering a wireless mouse.

Making boot disk

To make a quad-density floppy disk reliably, you have to perform 2 steps under pure DOS (or Windows 9x booted in "command prompt" mode, but not a DOS window), in a computer with a 1.2MB high-density 5.25" drive.
Contrary to many opinions in the Internet you usually don't have to make your floppy drive spin at 300 not 360rpm. I tested the following procedure on Digital, Citizen and Teac drives with success. So first, you need to get...

Boot package

Now:
1. Formatting the disk to Quad-density tracks
Use CopyQM to copy the CP/M-86 disk image to a disk. Do not use BAT file enclosed with disk image, as it may not work detecting drive incompatibility with QD disks, instead use CopyQM with CQMENU selecting "Direct hardware Access". This may not be needed in some drives. The CP/M disk may even be bootable in Siemens. Generally, we want to make a Quad Density formatted disk in High Density disk drive.
2. Record DOS on formatted disk
using the enclosed program copy the 720kB image into the disk by announcing

disktool write 720 211pg685.dsk B:

The resulting disk should be bootable in Siemens.

Boot from hard disk, new hard disk installation

An ordinary "MFM", like ST506/412 drive goes in, preferably 20MB ST225 (615/4/17 CHS). To make a hard disk bootable, use HDPARTY program from boot disk. First, low-level format the disk. Every MFM disk in a new controller should be low-level formatted. 25MB option is typical 615/4/17 geometry as for 20MB ST225 drive. This option will LLF the drive too. Then you will have a option to make a partition. It is possible to make partitions for DOS and CP/M, or you can make one single partition that fits all 20MB drive. After making the partition, use the option to make it active and exit the program. Reboot the computer.
Use HDINSTAL program, skip HDPARTY by pressing any key other than F8 in the appropriate step. The system will be copied and installed so the computer will be able to boot from hard disk. This DOs is more CP/M-like than MS-DOS and even some system calls are not PC compatible, so don't expect much software will work.
It is important that hard disk is present in this machine as drive B:, not C:, this is one of many remains from CP/M machine.

This machine boots by trying the floppy disk drive about once per second and flashing "SYSTEM" on screen. Then you can press space to get into on-ROM tests. When the hard disk spins up, computer will boot from it.
It is important that the disk will be left where it finished last read or write, and the computer is portable, so don't forget about parking drive's heads! There is also a HDPARK tool for hard disk heads parking. Use it when transporting the computer.
RTC is battery-backed but DOS always asks for time no matter what. This is because RTC is not so DOS-compatible.
This machine is NOT compatible with PC, so it won't run much software. The only bigger program I found useful on it was Derive 3.x. Many other programs interfere with Siemens' terminal settings (remember that it is a CP/M machine in its heart) making the graphics unreadable or causing black screen.
Under DOS, the floppy disk can read both 320kB disks and even 720kB quad-density disks. This format is rare in PC land, but it had its popularity in CP/M machines, in which 720kB of space on 5.25" disk was a luxury.

FUNCTION program can be used to define additional function keys.

ROM cartridge

The ROM cartridge is used to transfer data between computer and the industrial unit. It is important to use the cartridge intended for this machine, not for other machines as the connector stays the same and pinout or ROM banking may be changed. Generally, the ROM modules are accessible from STEP5 software tailored especially for this machine and I don't have tested any of this software.

Links:

- http://oldcomputers-ddns.org/public/pub/rechner/siemens/pg685/index.html - Some interesting files, manuals (in German) and CP/M related disk images.