Radio Shack TRS-80 Model 4 - Model 4 Port Bits

28
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 Disk DRQ from
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
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