BT848 ETC, BT848 Datasheet - Page 78

• Manufacturer Part Number: BT848
• Description: Single-Chip Video Capture for PCI
• Manufacturer: ETC

E
General Purpose I/O Port
Figure 29. GPIO Normal Mode
Figure 30. GPIO SPI Input Mode
68
LECTRICAL
Decoder
Decoder
Video
Video
I
NTERFACES
Scaler
Scaler
General Purpose I/O Port
The Bt848 provides a 24-bit wide general purpose I/O port. There are two modes
of operation for the GPIO port: normal mode and synchronous pixel interface
(SPI) mode. In the normal mode, the GPIO port is used as a general purpose port
enabling 24-bits of data to be input or output (Figure 29). In the SPI input mode,
the GPIO port can be used to input the video data from an external video decoder
and bypass the Bt848’s video decoder block (Figure 30). In the SPI output mode,
the output of the Bt848’s video decoder can be passed over the GPIO bus
(Figure 31), while being utilized by the rest of the Bt848 circuitry.
write enable pin. The GPINTR signal sets the bit in the interrupt register and caus-
es an interrupt condition to occur. The GPWE signal enables sampling of the data
on the GPIO port and places the data in an internal GPIO register. The polarity of
the GPWE pin is programmable.
GPINTR is sampled low upon release of the RST pin. This overrides the GPIO-
MOD bits in the GPIO/DMA control register and can only be returned to register
control by assertion of the RST pin while GPWE and GPINTR are in any other
states than high and low respectively. Care must be taken to ensure the state of
GPWE and GPINTR are configured correctly for the desired use of the GPIO pins.
Internal pullups are provided on both pins.
In addition to the 24 I/O bits, the GPIO port includes an interrupt pin, and a
The SPI output mode is automatically enabled if GPWE is sampled high and
Local Registers
Local Registers
Video Decoder
External
External
Circuitry
GPIO Port
GPIO Port
24 Bits of General I/O
Format Converter
Format Converter
Video Data
Video Data
L848A_A
FIFO
FIFO
Single-Chip Video Capture for PCI
and PCI Initiator
and PCI Initiator
DMA Controller
DMA Controller
Bt848/848A/849A
Brooktree
®