Interfacing to Apple LocalTalk Networks
Design note for interfacing with Apple LocalTalk networks using LTC1323 and LTC491 transceivers to replace dual-supply bipolar solutions with single-supply ICs.
Overview
This design document outlines hardware implementations for Apple LocalTalk (AppleTalk) network connections using Linear Technology interface ICs. It highlights the transition from legacy bipolar AM26LS30/AM26LS32 two-chip solutions requiring external -5V supplies to integrated single-supply solutions. The text details the use of the LTC1323, which includes an internal charge pump to generate its own negative supply while meeting EIA RS422 and EIA 562 standards. It also provides design considerations for PhoneNet applications using the LTC1323CS16 and LTC491, as well as recommendations for EMI filter optimization to maintain signal integrity over twisted-pair cabling.
Use Cases
- AppleTalk network hardware interface
- Battery-powered RS422 communication
- PhoneNet compatible network nodes
- Single-supply serial I/O design
Topics
Referenced Parts
Advanced Micro Devices
The original LocalTalk hardware design uses an AM26LS32 chip for the receivers
LTC1323
Linear Technology
The LTC1323 uses the differential driver output stage of Figure 2.
LTC1323CS16
Linear Technology
the LTC1323CS16 can be used as shown in Figure 3.
LTC1323CS24
Linear Technology
A better solution is to use the LTC1323CS24 which provides a complete low power serial I/O interface
LTC491
Linear Technology
the LTC491 can be used as shown in Figure 4. Only RS485 drivers will work in this application.
| AM26LS30 | Advanced Micro Devices | an AM26LS30 chip for the drivers of a LocalTalk port. |
| AM26LS32 | Advanced Micro Devices | The original LocalTalk hardware design uses an AM26LS32 chip for the receivers |
| LTC1323 | Linear Technology | The LTC1323 uses the differential driver output stage of Figure 2. |
| LTC1323CS16 | Linear Technology | the LTC1323CS16 can be used as shown in Figure 3. |
| LTC1323CS24 | Linear Technology | A better solution is to use the LTC1323CS24 which provides a complete low power serial I/O interface |
| LTC491 | Linear Technology | the LTC491 can be used as shown in Figure 4. Only RS485 drivers will work in this application. |