LM1238 National Semiconductor Corporation, LM1238 Datasheet
LM1238
Available stocks
Related parts for LM1238
LM1238 Summary of contents
Page 1
... CRT display. Four I2C compatible DACs are available to control monitor bias and brightness circuits. The LM1238 preamp is designed to be 100% compatible with the LM246x high gain driver family and the LM2479/80 Clamp ICs. ...
Page 2
Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage, Pins 15 and 19 Peak Video DC Output Source Current (Any One Amp) Pins 18 ...
Page 3
Video Signal Electrical Characteristics Unless otherwise noted 25˚ numbers refer to the definitions in Table 1. See Note 7 for Min and Max parameters and Note 6 for Typicals. Symbol Parameter A Track Gain Change between ...
Page 4
DAC Output Electrical Characteristics Unless otherwise noted 25˚ for Min and Max parameters and Note 6 for Typicals. DAC parameters apply to all 4 DACs. Symbol Parameter (V ) Variation in voltage of DAC with ∆V ...
Page 5
... Note 15: A minimum pulse width of 200 ns is the guaranteed minimum for a horizontal line of 15 kHz. This limit is guaranteed by design lower line rate is used then a longer clamp pulse may be required. Note 16: Adjust input frequency from 10 MHz (A Note 17: Once the spot killer has been activated, the LM1238 remains in the off state until V Hexadecimal and Binary Notation Hexadecimal numbers appear frequently throughout this document, representing slave and register addresses, and register values. These appear in the format “ ...
Page 6
... In addition, the Horizontal blanking input also assists in setting the proper cathode black level, along with the Clamp- ing pulse. The Vertical blanking input initiates a blanking level at the LM1238 outputs which is programmable from 3 to 127 lines (we recommend at least 10). This can be op- tionally disabled so there is no vertical blanking. ...
Page 7
... LM2469 driver. ABL GAIN REDUCTION The ABL function reduces the contrast level of the LM1238 as the voltage on pin 22 is lowered from V volts. Figure 8 shows the amount of gain reduction as the voltage is lowered from V is small until V slope increases ...
Page 8
... External resistor, 10k 1%, sets the internal bias current level for optimum performance of the LM1238. This resistor should be placed as close to pin 3 and the pin 4 ground return as possible. This is the ground for the analog portions of the LM1238 internal circuitry. ...
Page 9
... A resistor of at least 100Ω should be connected in series with these outputs for additional ESD protection. Ground pin for the digital portion of the LM1238 circuitry, and power supply pin for both analog and digital sections of the LM1238. Note the recommended charge storage and high frequency capacitors which should be as close to pins 17 and 18 as possible ...
Page 10
... CRT capacitance (averaged by C begins to turn off and the voltage at pin 22 begins to drop. The LM1238 then lowers the gain of the three video channels until the beam current reaches an equilibrium value. This pin accepts either TTL or CMOS logic levels ...
Page 11
Schematic Diagram FIGURE 9. LM123x-LM246x Demo Board Schematic 11 20038716 www.national.com ...
Page 12
Schematic Diagram FIGURE 10. LM123x-LM246x Demo Board Schematic (continued) www.national.com 12 20038717 ...
Page 13
PCB Layout FIGURE 11. LM123x-LM246x Demo Board Layout 13 20038718 www.national.com ...
Page 14
... OSD Constant Character Height Function A constant height function is included in the LM1238 to maintain a constant OSD height as the number of horizontal www.national.com 12 is used to display one (or one set) of the available icons which would correspond to the adjustment being carried out ...
Page 15
OSD Operation (Continued) FIGURE 13. The First 8 Icon Sets (0-7) 15 20038763 www.national.com ...
Page 16
OSD Operation (Continued) www.national.com FIGURE 14. Last 8 Icon Sets (8-15) 16 20038762 ...
Page 17
... Acknowledge bit. The next 8 bits will be the read data driven out by the LM1238 preamp associated with the ad- dress indicated by the two address bytes. Subsequent read data bytes will correspond to the next increment address locations. Data should only be read from the LM1238 when both OSD windows are disabled. 17 20038726 ...
Page 18
Microcontroller Interface www.national.com (Continued) 2 FIGURE 16 Compatible Read Sequence 18 20038727 ...
Page 19
... LM1238 Address Map Address Range R/W 0x0800h-0x0805h R/W 0x0810h-0x081Fh R/W 2 Pre-Amp Interface I C Registers TABLE 4. LM1238 Pre-Amplifier Interface I Register Address BGAINCTRL 0x0810 GGAINCTRL 0x0811 RGAINCTRL 0x0812 CONTRCTL 0x0813 DAC2CTRL 0x0814 DAC3CTRL 0x0815 DAC1CTRL 0x0816 DAC4CTRL 0x0817 DCF/OSD-Con/DC 0x0818 GLOBALCTRL 0x0819 CLMP/PLL/VBL/OOR 0x81E SRTSTCTRL 0x81F ...
Page 20
Control Register Definitions Bits 7–3 Bar Indicator. These five bits determine the length of the bar indicator on a scale of 0–31. A value of 0 results in no indicator. 31 results in a full scale ...
Page 21
Control Register Definitions Icon Alternate Period Control Register (I Register Name (address): ALT (0x0804h RSV RSV Bits 3–0 Icon Alternate Period. These four bits set the period at which the icon will switch between images, in increments of ...
Page 22
Control Register Definitions 2 Contrast Control Register (I C address 0x0813h) Register Name (address): CONTRCTRL (0x0813h RSV CO Bits 6–0 Contrast Gain Control. These seven bits determine the overall gain of all the three channels. Bit 7 Reserved. ...
Page 23
... When set to 1, the H flyback pulse will be gated off. Bit 5 Clamp Polarity. Determines the polarity of the clamp signal used by the LM1238. When this bit is 0 (default) the LM1238 requires a positive clamp signal. When this bit is 1, the LM1238 requires a negative going clamp signal. ...
Page 24
... NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant ...