SC144, v1.1, User Guide

SC144 is dual function real time clock and I2C bus master interface card designed for the Z50Bus.

SC144 RTC and I2C bus master

This module provides a real time clock and calendar using a battery backed DS1302+ integrated circuit. It also provides a 5-volt bit-bang I2C bus master.

A variety of connectors are included for the I2C making it easy to connect to the SC400 series of I2C modules as well as to many other I2C devices.

SC400 series I2C modules


This card occupies one input / output address location. This can be set with jumper, JP1.

JP1, as illustrated to the left, provide jumper positions for all 8 I/O address bits.

Fit jumper shunts to any bit position you require to be high.

For example, to set the address to 0x0C (binary 0000 1100) fit a shunt to bit 2 and another to bit 3.

The current software assumes the address is 0x0C. This may change in the future as the recommended I/O map for Z50Bus systems is to have the processor or SBC use the lower 64 I/O addresses.

Bus signals

The two I2C signals, SCL and SDA, can optionally be connected to the Z50Bus USER signals USER0 and USER3, using jumpers JP2 and JP3.

Jumper shunts should only be fitted to JP2 and JP3 if you require the I2C signals to be output to the Z50Bus.

As the USER pins of the bus can be used for any purpose it is important to ensure that there are no other cards in the system that are using the pins for different signals.

Firmware support

Currently, the only firmware (ROM based) support is in RomWBW. This fully supports the real time clock (RTC) and does not any specific support for the I2C bus. Both the RTC and the I2C bus can of course be accessed directly with your own software.

Light Emitting Diodes (LEDs)

The card has LEDs to show the state of the I2C serial data (SDA) and serial clock (SCL) signals. The LEDs light when the signals are low.

Example I2C software

The SC400 series of I2C modules is supported by and example / test program. This program has been written for use from the Small Computer Monitor.

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