Repair manual

2-30
THEORY OF OPERATION
3. Random Access Memory (RAM)
The Digital Palette uses two types of Random Access Memory: Dynamic Read
Address Memory (DRAM) and Video Random Access Memory (VRAM).
The DRAM memory receives and stores the commands and pixel image data via
the applicable parallel interface from the host computer. Its the exposure
sequence (Start Exposure, Parameters, Expose Color, Pixel Image Data for a
particular color, and Terminate Exposure) that is loaded into the DRAM’s.
The VRAM is the exposure memory. It momentarily stores the pixel image data
when it is downloaded from the DRAM memory.
a. Dynamic Random Access Memory (DRAM) (Figure 2-9, sheet 1)
The basic Digital Palette Configuration uses 256K of DRAM (four
64K x 4-Bit DRAM’s) as its storage memory. The Digital Palette can
accomodate an additional 512K of DRAM (four optional 256K x 4-Bit
DRAM’s).
The DRAM address bus (RA0 - RA7) is generated by two RAM control
PAL’s in the RAM Control circuit. Its data lines are connected directly to
the Address/Data Communications Bus. Select signals (control lines) are
generated by the PAL’s in the RAM Control circuit. Refer to paragraph c
for a functional description of the RAM Control circuit.
b. Video Random Access Memory (VRAM) (Figure 2-9, sheet 2)
The basic Digital Palette Configuration uses 128K of VRAM (four
64K x 4-Bit VRAM’s) as its exposure memory. The Digital Palette
can accomadate an additional 128K of VRAM (four optional 64K x 4-Bit
VRAM’s).
The VRAM address bus (RA0 - RA7) is generated by two RAM control
PAL’s in the RAM Control circuit. Its data lines are connected directly to
the Address/Data Communications Bus. Select signals (control lines) are
generated by the PAL’s in the RAM Control circuit. Refer to paragraph c
for a functional description of the RAM Control circuit.
The basic Digital Palette Configuration (128K of VRAM) provides the
ability to expose images with a horizontal resolution of 512 to 2048
pixels. This configuration of the Digital Palette uses four 64K x 4
VRAM’s.