Radio Shack TRS-80 Model 4 Technical Reference Manual

90
PORT EAH OUTPUT BITS WITH UART CONTROL REGISTER DISABLED
DATA BIT FUNCTION
D7 Not Used
D6 Not Used
D5 Secondary unassigned, Pin 18 DB-25
D4 Secondary Transmit Data, Pin 14 DB-25
D3 Secondary Request To Send, Pin 19 DB-25
D2 Break 0 = disable Transmit Data (continuous space)
D1 Data Terminal Ready, Pin 20 DB-25
D0 Request To Send, Pin 4 DB-25
PORT EAH INPUT BITS
DATA BITS FUNCTION
D7 Data Received, 1 = condition true
D6 Transmitter Holding register empty, 1 = condition true
D5 Overrun error, 1 = condition true
D4 Framing error, 1 = condition true
D3 Parity error, 1 = condition true
D2 Not Used
D1 Not Used
D0 Not Used
PORT
EBH
OUTPUT:
TRANSMITTER HOLDING REGISTER
INPUT:
RECEIVER HOLDING REGISTER
An output to this port loads the UART Transmitter Holding register with a word to be transmitted, as soon as the
last word loaded in the holding register is transmitted. This register should never be loaded until the Transmitter
Holding register empty bit (port EAH) is true. An input from this port reads the last word received from the UART
received data holding register. This register should not be read until the data received bit (port EAH) is true.

Radio Shack TRS-80 Model 4 Specifications

General

Brand	Radio Shack
Model	TRS-80 Model 4
Category	Desktop
Language	English