7.3.25 CR1E
(Reserved). The default value of this register after power up is 80H.
7.3.26 CR1F
(Reserved). The default value of this register after power up is 00H.
7.3.27 CR20
(Reserved). The default value of this register after power up is 3CH.
7.3.28 CR21 - CR22
Registers CR21 - CR22 are Reserved. Reserved bits cannot be written and return 0 when read.
7.3.29 CR23
CR23 can only be accessed in the configuration state and after the CSR has been initialized to 23H. The default
value of this register after power up is 00H (Table 41). CR23 is used to select the base address of the parallel port.
If EPP is not enabled, the parallel port can be set to 192 locations on 4-byte boundaries from 100H - 3FCH; if EPP is
enabled, the parallel port can be set to 96 locations on 8-byte boundaries from 100H - 3F8H (Table 42). To disable
the parallel port, set ADR9 and ADR8 to zero.
Parallel Port Address Decoding: nCS = ’0’ and A10 = ’0’ are required to access the Parallel Port when in Compatible,
Bi-directional, or EPP modes. A10 is active when in ECP mode.
Table 41 - CR23: Parallel Port Base Address Register
DB7
ADR9
DB6
ADR8
DB5
DB4
DB3
DB2
DB1
ADR3
DB0
ADR2
ADR7
ADR6
ADR5
ADR4
Table 42 - Parallel Port Addressing Options
EPP ENABLED
ADDRESSING (LOW BITS) DECODE
A[1:0] = XXb
A[2:0] = XXXb
No
Yes
7.3.30 CR24
CR24 can only be accessed in the configuration state and after the CSR has been initialized to 24H. The default
value of this register after power up is 00H (Table 43). CR24 is used to select the base address of Serial Port 1
(UART1). The serial port can be set to 96 locations on 8-byte boundaries from 100H - 3F8H. To disable Serial Port
1, set ADR9 and ADR8 to zero. Set CR24.0 to 0 when writing the UART1 Base Address.
Serial Port 1 Address Decoding: nCS = ’0’ and A10 = ’0’ are required to access UART1 registers. A[2:0] are decoded
as XXXb.
Table 43 - CR24: UART1 Base Address Register
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
ADR9
ADR8
ADR7
ADR6
ADR5
ADR4
ADR3
0
7.3.31 CR25
CR25 can only be accessed in the configuration state and after the CSR has been initialized to 25H. The default
value of this register after power up is 00H (Table 44). CR25 is used to select the base address of Serial Port 2
(UART2). Serial Port 2 can be set to 96 locations on 8-byte boundaries from 100H - 3F8H. To disable Serial Port 2,
set ADR9 and ADR8 to zero. Set CR25.0 to 0 when writing the UART2 Base Address.
Serial Port 2 Address Decoding: nCS = ’0’ and A10 = ’0’ are required to access UART2 registers. A[2:0] are decoded
as XXXb.
SMSC DS – SP37E760
Page 55
Rev. 04/13/2001
SMSC [ SMSC CORPORATION ]
