National Instruments PCI-1200 用户手册
Chapter 4
Theory of Operation
© National Instruments Corporation
4-13
All three ports on the 82C55A are TTL-compatible. When enabled, the
digital output ports are capable of sinking 2.5 mA of current and sourcing
2.5 mA of current on each digital I/O line. When the ports are not enabled,
the digital I/O lines act as high-impedance inputs.
digital output ports are capable of sinking 2.5 mA of current and sourcing
2.5 mA of current on each digital I/O line. When the ports are not enabled,
the digital I/O lines act as high-impedance inputs.