Mallinckrodt NELLCOR NPB-4000 Service Manual page 154

Section 14: Main Color Board Digital Theory of Operation
14.8.2 LCD DISPLAY RAM
14-14
The above signals are all of the signals used to interface to the 386EX for
transferring of data to and from the control registers and the display ram.
There are some general purpose I/O ports that are under software control. They
can be programmed as inputs or outputs. Two of these ports are being used
(GPIO4 and GPIO5) as outputs and the rest are not being used. If GPIO4 is set,
information is displayed left to right. If GPIO4 is cleared, information is
displayed right to left. If GPIO5 is set, information is displayed top to bottom.
If GPIO5 is cleared, information is displayed bottom to top. The software will
program GPIO4 & 5 to be set. The unused ports are pulled-down with 1k ohm
resistors on the main board. There is one general purpose output port (pin 106).
It is not being used.
The interface signals for the display RAM are prefaced with the letters VID,
which implies video ram. The interface to the display ram (VIDRAM) is defined
in the SED1354 Hardware Functional Specification manual and is connected
directly to the DRAM.
The LCD display interfaces directly with the SED1354 through the 74HCT244
buffers. The signals used are DRDY, FPFRAME, FPLINE, FPSHIFT, and
FPDATA[15:0].
The FPLINE signal is the line pulse, which indicates the start of a line. It is an
active low signal. The FPFRAME signal is the frame pulse, which indicates a
start-of-frame. It is an active low signal. FPSHIFT is the data shift clock and the
LCD display stores the data on the falling edge of this clock. DRDY is the
display enable output signal. It indicates when data is ready for each line of
video. It is an active high signal. It goes high when data for the line is valid and
stays high until the line is finished. FPDATA[15:0] generate the RED, BLUE,
GREEN video information and are defined as follows;
FPDATA[15] is Blue bit 1
FPDATA[14] is Blue bit 2
FPDATA[13] is Green bit 0
FPDATA[12] is Green bit 1
FPDATA[11] is Green bit 2
FPDATA[10] is Red bit 1
FPDATA[9] is Red bit 2
FPDATA[8] is Blue bit 3
FPDATA[7] is Blue bit 4
FPDATA[6] is Blue bit 5
FPDATA[5] is Green bit 3
FPDATA[4] is Green bit 4
FPDATA[3] is Green bit 5
FPDATA[2] is Red bit 3
FPDATA[1] is Red bit 4
FPDATA[0] is Red bit 5
The 1354 can only support 64,000 colors, therefore Red bit 0 and Blue bit 0 are
not supported and are tied to ground through 1k ohm pull-down resistors (R515
and R516).