Radio Shack TRS-80 III - Page 66

PORT EAH OUTPUT BITS WITH UART CONTROL REGISTER DISABLED
DATA BIT
D7
D6
D5
D4
D3
D2
D1
D0
DATA BITS
D7
D6
D5
D4
D3
D2
D1
D0
FUNCTION
Not
Used
Not Used
Secondary unassigned, Pin 18 DB-25
Secondary Transmit Data,
Pin 14 DB-25
Secondary Request
To Send, Pin 19 DB-25
Break 0 =disable Transmit Data (continous space)
Data Terminal Ready, Pin 20 DB-25
Request To Send, Pin 4 DB-25
PORT EAH INPUT BITS
FUNCTION
Data Received,
1 =condition true
Transmitter Holding register empty, 1 =condition true
Overrun error,
1 = condition true
Framing error, 1 =condition true
Parity error, 1 = condition true
Not Used
Not Used
Not Used
58
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.