initialized to 04H. The default value after power
up is 00H.
CR04
This register can only be accessed in the
Configuration Mode and the CSR has been
Table 51 - CR04 - Parallel and Serial Extended Setup Register
BIT NO.
BIT NAME
DESCRIPTION
1,0
Parallel Port
Extended Modes
Bit 1
0
Bit 0
0
If CR1 bit 3 is a low level then:
Standard and Bidirectional Modes (SPP)
(Default)
0
1
1
1
0
1
EPP Mode and SPP
ECP Mode (Note CR4_2)
ECP Mode & EPP Mode (Note CR4_1, 2)
2,3
Parallel Port
FDC
Refer to Parallel Port Floppy Disk Controller description.
Bit 3
Bit 2
0
0
1
1
0
1
0
1
Normal
PPFD1
PPFD2
Reserved
4
5
MIDI 1
MIDI 2
Serial Clock Select Port 1: A low level on this bit, disables MIDI
support, clock = divide by 13 (Default). A high level on this bit
enables MIDI support, clock = divide by 12. (Note CR4_3)
Serial Clock Select Port 2: A low level on this bit, disables MIDI
support, clock = divide by 13 (Default). A high level on this bit
enables MIDI support, clock = divide by 12. (Note CR4_3)
6
7
EPP Type
ALT I/O
0 = EPP 1.9 (Default)
1 = EPP 1.7
1 = use pins IRRX2, IRTX2 (pins 25, 26)
0 = use pins IRRX, IRTX (Default) (pins 88, 89)
note: If this bit is set, the Infrared receive and transmit functions
will not be available on pins 25 and 26 unless
bits [0,1] of CR00 are set to [1,1].
Note CR4_1: In this mode, EPP can be selected through the ecr register of ECP as mode 100.
Note CR4_2: In these modes, 2 drives can be supported directly, 3 or 4 drives must use external 4 drive
support. SPP can be selected through the ecr register of ECP as mode 000.
Note CR4_3: MIDI Support: The Musical Instrumental Digital Interface (MIDI) operates at 31.25Kbaud (+/-1%)
which can be derived from 125KHz. (24MHz/12=2MHz, 2MHz/16=125kHz).
124
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