CR27
CR27 can only be accessed in the configuration state and after the CSR has been initialized to 27H. The default
value of this register after power up is 00H (Table 112). CR27 is used to select the IRQ for the FDC (Bits 4 - 7) and
the Parallel Port (bits 3 - 0). Any unselected IRQ output (registers CR27 - CR29) is in tri-state.
Table 112 - CR27: FDC and PP IRQ Selection Register
D3-D0
OR
D7-D4
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
IRQ SELECTED
NONE
IRQ_1
IRQ_2
IRQ_3
IRQ_4
IRQ_5
IRQ_6
IRQ_7
IRQ_8
IRQ_9
IRQ_10
IRQ_11
IRQ_12
IRQ_13
IRQ_14
IRQ_15
CR28
CR28 can only be accessed in the configuration state and after the CSR has been initialized to 28H. The default
value of this register after power up is 00H. CR28 is used to select the IRQ for Serial Port 1 (bits 7 - 4) and for Serial
Port 2 (bits 3 - 0). Refer to the IRQ encoding for CR27 (Table 113). Any unselected IRQ output (registers CR27 -
CR29) is in tristate. Shared IRQs are not supported in the FDC37N3869.
Table 113 - UART Interrupt Operation
UART1
UART2
IRQ PINS
UART1
OUT2 bit
UART1 IRQ
UART2
OUT2 bit
UART2 IRQ
UART1
Pin State
UART2
Pin State
Output State
Output State
0
1
1
0
0
1
1
1
1
Z
0
0
0
1
1
1
1
1
1
Z
Z
Z
Z
1
0
Z
Z
1
1
0
0
Z
Z
Z
1
0
1
0
1
0
asserted
de-asserted
Z
asserted
de-asserted
asserted
de-asserted
asserted
de-asserted
Z
asserted
asserted
de-asserted
de-asserted
It is the responsibility of the software to ensure that two IRQ’s are not set to the same IRQ
number. Potential damage to chip may result. Note: Z = Don’t Care.
SMSC DS – FDC37N3869
Page 111
Rev. 10/25/2000
SMSC [ SMSC CORPORATION ]
