Rs-232-C Interfaces - NCR PC4I Technical Reference

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RS-232-C IBTERFACES

The modem and video interfaces of the Videotex

adapter are controlled by two separate 2651 USART

integrated circuits, used in the asynchronous

receiver/transmitter mode.

The registers of each of these Programmable

Communications Interfaces (PC!s) are memory mapped in

the address ranges ODC200H-ODC207H (modem) and

ODC300H-ODC307H (video). The precise memory map for

the modem interface is given below. Corresponding

addresses for the video interface are mapped in the

higher area.

USART Register

Read Receive Holding Register

Reed Status Register

Read Mode Register 1/2

Reed Commend Register

Write Transmit Holding Register

Write SYNC1, SYNC2,

Transmitter/Receiver Mode Register 2

Write Command Register

The remaining sections of this Chapter deal with the

programmable features of the PCI, followed by an

explanation of its use by the Videotex and modem