AComm.Dll

1995, 1997 — Automatic Data Processing, Inc.

Introduction

When ADP began creating their AutoPay product suite to replace the Payroll, they needed a communications module to perform the communications tasks over the modem to their mainframes. They brought me in to design and implement a 16-bit Windows DLL and test application to fit this need.

Architecture

After our initial meeting, we decided on the following design:

C (not C++) DLL interface
No UI in the DLL -- all communication with the user would be via the calling application and the DLL interface
One set of functions to perform Datapool Offload file transfer services (based on ZMODEM protocol)
One set of functions to perform Check-Mate with the ADP mainframe (IBM 3101 terminal)
Modem communications using standard AT commands and a user-definable initialization string with auto-detect

Development

A state machine was written to control the modem, using generic AT commands. At this time, Windows 3.1 didn't recognize modems at the OS level, and TAPI hadn't been born yet.

A terminal emulation class was developed to interact with Check-Mate as if we were an IBM 3101 terminal (which is how Check-Mate was originally used). I had to reverse-engineer the screen formats, and develop a sort of scripting capability to programmatically control the terminal session.

Armed with the source code for PC Payroll's modified ZMODEM code, I ported it to use our communication class methods.

The DLL and test application were developed according to ADP's CSS coding standards, using Microsoft Visual C++, and totaled over 25,000 lines of code.

Technologies

C++ and MFC were the language and library used -- statically linked
SQL was used in creating the "IO Classes" to communicate with the database. The product supported multiple database engines
An AT Command Set state machine was used to control the modem
IBM 3101 Terminal Emulation with scripting engine was developed for Check-Mate
A ZMODEM derivative was the basis for the Datapool Offload file transfer services

Conclusion

The project contained over 25,000 lines of code. AComm.Dll was later upgraded to WIN32, and a modem auto-detect was added. TAPI support was added in 1997, and was the basis for the ACommServer project in 2000.