Read/write realtime clock chip

Supported Cards

• Turner Hall Publishing by Symantec
  • Memory expansion: 256K
  • RTC: NEC uPD1990AC @2c0h-2c2h
• CTE Research 410B (New for version 2.0)
  • Multi-function I/O card
  • RTC: NEC uPD4990AC @240h

Turner Hall Publishing by Symantec

The board is an 8-bit ISA memory expansion and RTC card from Turner Hall Publishing.

I couldn't find a driver for its RTC chip (NEC uPD1990AC) so I decoded the bus I/O port (see PDF) and wrote my own program to read/write the clock.

This clock chip does not store the year! The program writes NECCLOCK.BIN in the current working directory to recover the year on the next reboot. It does handle a new year rollover that might occur while the machine is off. It also handles leap years. If the computer is not booted at least once a year, the year it sets will be off by the number of years it hasn't been booted (less one).

CTE Research 410B

User siordon was looking for a program to read/write the RTC (NEC uPD4990AC) on this card and asked if NECCLOCK would work. It did not work because the I/O port address and registers are different. However, the chip is backwards compatible so we traced the I/O lines on the card (see PDF) and added support to NECCLOCK for reading and writing the RTC.

This RTC does store the year and handles leap years so NECCLOCK.BIN is not created or used.

Special thanks to siordon for all the hardware tracing and software testing!

Assembly Instructions

The source is written to be assembled with Microsoft Assembler (MASM) and Linker (LINK).

C> MASM NECCLOCK
C> LINK NECCLOCK

Usage

Usage: C> NECCLOCK <flags>

Card select flags:
/ct         Turner Hall Publishing 256KB memory expansion w/NEC uPD1990AC RTC
/cc         CTE Research CTE-410B multi-function I/O w/NEC uPD4990AC RTC

Function flags:
            Print RTC time
/s          Write RTC to DOS date/time
/i          Write DOS date/time to RTC