HD6845SP Renesas Electronics America, HD6845SP Datasheet - Page 3

• Manufacturer Part Number: HD6845SP
• Description: CRT Controller
• Manufacturer: Renesas Electronics America

Specifications of HD6845SP

• Power Supply Type: Analog
• Typical Operating Supply Voltage: 5 V
• Minimum Operating Supply Voltage: 4.75 V
• Maximum Operating Supply Voltage: 5.25 V

Linear address generates refresh memory address MA0-MA13 to be used for refreshing the screen. By these address
signals, refresh memory is accessed periodically. As 14 refresh memory address signals are prepared, 16k words max are
accessible. Moreover, the use of start address register enables paging and scrolling. Light pen detection circuit detects light
pen position on the screen. When light pen strobe signal is received, light pen register memorizes linar address generated
by linear address generator in order to memorize where light pen is on the screen. Cursor control circuit controls the
position of cursor, its height, and its blink.
Figure 6 Internal Block Diagram of CRTC
* FUNCTION OF SIGNAL LINE
The CRTC provides 13 interface signals to MPU and 25 interface signals to CRT display.
* Interface Signals to MPU
Bi-directional Data Bus (D0-D7)
I/O Pin No. 33-26
Bi-directional data bus (D0-D7) are used for data transfer between the CRTC and MPU. The data bus outputs are 3-state
buffers and remain the high-impedance state except when MPU performs a CRTC read operation.
Read/Write /W / R
Input Pin No.22
Read/Write signal (/W / R) controls the direction of data transfer between the CRTC and MPU. When /W / R is at "High"
level, data of CRTC is transferred to MPU. When /W / R is at "low" level, data of MPU is transferred to CRTC.
Chip Select (/CS)
Input Pin No. 25
Chip Select signal (/CS) is used to address the CRTC. When /CS is at a "low" level, it enables Read/Write operation in
CRTC internal registers. Normally this signal is derived from decoding address signal of MPU under the condition that
VMA of MPU is at "High" level.
Register Select
Input Pin No. 24
Register Select signal (RS) is used to select the address register and 18 control registers of the CRTC. When RS is at "low"
level, the address register is selected and when RS is at "high" level, control registers are selected. This signal is normally a
derivative of the lowest bit (A0) of MPU address bus.
Enable (E)
Input Pin No. 23
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