DS1302 Real Time Clock for the RC2014 computer
The board
RomWBW has code to support a DS1302 Real Time Clock, enabling files to be timestamped and other timekeeping operations. This board implements the clock in a standard way for the RC2014.
The design is largely based on the clock implementation on the RetroBrew Computers SBC V2 and Zeta SBC V2.
What can you use this for?
Telling the time :)
Getting started with RomWBW
Set DSRTCENABLE to true in the configuration and rebuild your ROM image.
On startup you will see the time shown.
ZSystem has more complete support for time utilities than CP/M. After booting into ZSystem by pressing Z, Run ldds to load the resident time driver. td can then be used to set the time as well as view it.
In CP/M RTC.com can be used for querying and setting the clock but it is very basic.
Jumpers
SW1 - Address configuration. For the default address of 0xC0, set switches 5 and 6 to on.
Bill Of Materials
| Reference | Value | Farnell part no | Rapid part no | Digi-key part no |
|---|---|---|---|---|
| P1 | 1x39 right angled pin header | 732-5350-ND | ||
| BT1 | Keystone 106 20mm battery holder for CR2032 | 1650672 | 36-106-ND | |
| BT1 | CR2032 battery | P189-ND | ||
| U1 | CD74HCT688E COMPARATOR, SINGLE, PDIP-20 | 2407104 | 296-2131-5-ND | |
| U2 | SN74HCT125N LOGIC, BUS BUFF TRI-ST QD, 14DIP | 1739676 | 296-8386-5-ND | |
| U3 | CD74HCT174E 74HCT CMOS, 74HCT174, DIP16, 5.5V | 1105983 | 296-2100-5-ND | |
| U4 | DS1302N+ RTC W/ RAM, 248B, D-D-M-Y, HH:MM:SS, DIP | 2515367 | DS1302N+-ND | |
| U5 | SN74HCT32N IC, QUAD 2-INPUT OR, 74HCT32, DIP14 | 9591982 | 296-1615-5-ND | |
| C1-5 | 0.1uF MLCC capacitor | BC2665CT-ND | ||
| Y1 | 32.768 kHz crystal | 9712887 | 535-9034-ND | |
| RN1 | 10k 8 Pin Commoned Resistor Network | 63-0125 | 4608X-1-103LF-ND | |
| SW1 | 6 way DIL switch | 80-0338 | CT2066-ND | |
| U1 | CONN IC DIP SOCKET 20POS TIN | AE10015-ND | ||
| U2 | CONN IC DIP SOCKET 14POS TIN | AE10012-ND | ||
| U3 | CONN IC DIP SOCKET 16POS TIN | AE10013-ND | ||
| U4 | CONN IC DIP SOCKET 8POS TIN | AE10011-ND | ||
| U5 | CONN IC DIP SOCKET 14POS TIN | AE10012-ND |
Construction tips
The footprint for the battery holder is designed for a Keystone 106, other battery holders should work if the pins are ~20.5mm apart, which seems to be fairly standard.