Model 4 Port Bits - Radio Shack TRS-80 Model 4 Technical Reference Manual

3.3 Model 4 Port Bits

Name: WRNMIMASKREG*
Port Address: 0E4H
Access: WRITE ONLY
Bit 7 = ENINTRO; 0 disables Disk INTRQ from
generating an NMI.
1 enables above.
Bit 6 = ENDRQ; 0 disables
generating an NMI.
1 enables above.
Name: RDNMISTATUS*
Port Address: 0E4H
Access: READ ONLY
Bit 7 = Status of Disk INTRQ; 1 = False, 0 = True
Bit 6 = Status of Disk DRO; 1 False, 0 = True
Bit 5 = Reset* Status; 1 = False, 0 = True
Name: MOD OUT
Port Address: 0ECH
Access: WRITE ONLY
Bit 7 = Undefined
Bit 6 = Undefined
Bit 5 = DISWAIT; 0 disables video waits, 1 enables
Bit 4 = ENEXTIO; 0 disables external 10 Bus,
1 enables
Bit 3 = ENALTSET; 0 disables alternate character
set,
1 enables alternate video character set.
Bit 2 = MODSEL; 0 enables 64 character mode,
1 enables 32 character mode.
Bit 1 = CASMOTORON; 0 turns cassette motor off,
1 turns cassette motor on.
Bit 0 = Undefined
Disk DRQ from
28
Name: RDINTSTATUS*
Port Address: 0E0H
Access: READ ONLY
NOTE: A 0 indicates the device is interrupting.
Bit 7 = Undefined
Bit 6 = RS-232 ERROR INT
Bit 5 = RS-232 RCV INT
Bit 4 = RS-232 XMIT INT
Bit 3 = IOBUS INT
Bit 2 = RTC INT
Bit 1 = CASSETTE (1500 Baud) INT F
Bit 0 = CASSETTE (1500 Baud) INT R
Name: CASOUT
Port Address: 0FFH
Access: WRITE ONLY
Bit 7 = Undefined
Bit 6 = Undefined
Bit 5 = Undefined
Bit 4 = Undefined
Bit 3 = Undefined
Bit 2 = Undefined
Bit 1 = Cassette output level
Bit 0 = Cassette output level