4820SX/T (250-5140) Settings Faxback Doc. # 1663 The main logic board of your computer has a DIP switch with four switches. On the Tandy 4820 SX/T, the default setting for switches 1 and 2 are OFF. These switches are reserved for use when the processor is upgraded. Switch 3 is used to indicate the type of video display adapter installed (monochrome or color). The default setting is ON (color). Change the setting to OFF only if you install a monochrome display adapter as the primary video display adapter. Use a pen or other pointed object to set the switch. Switch 4 is reserved. Switch settings are shown in the following tables: ┌──────────────┬──────────────┬──────────┬────────┐ │ Processor │ SWITCH 1 │ SWITCH 2 │ SOCKET │ ├──────────────┼──────────────┼──────────┼────────┤ │ 486SX │ OFF │ OFF │ U54 │ ├──────────────┼──────────────┼──────────┼────────┤ │ 486DX │ ON │ OFF │ U54 │ ├──────────────┼──────────────┼──────────┼────────┤ │ 487SX │ ON │ ON │ U54 │ ├──────────────┼──────────────┼──────────┼────────┤ │*486 Overdrive│ ON │ ON │ U54 │ ├──────────────┼──────────────┼──────────┼────────┤ │ 486DX2/ODPR │ ON │ OFF │ U54 │ ├──────────────┼──────────────┼──────────┼────────┤ │ 487SX │ OFF │ OFF │ U55 │ ├──────────────┼──────────────┼──────────┼────────┤ │*486 Overdrive│ OFF │ OFF │ U55 │ └──────────────┴──────────────┴──────────┴────────┘ * Note: Installing an Overdrive 25/50 Processor will only increase the CPU speed to 40MHz, not 50MHz. TCH 3 (Primary Video Display Adapter Type) ┌──────────┬──────────────────────────┐ │ SWITCH 3 │ DISPLAY ADAPTER TYPE │ ├──────────┼──────────────────────────┤ │ ON │ color* │ ├──────────┼──────────────────────────┤ │ OFF │ monochrome │ ├──────────┴──────────────────────────┤ │ * Indicates default setting. │ └─────────────────────────────────────┘ JUMPERS AND DIP SWITCHES This section explains how to change the operation of the VGA 1024 NI Adapter by re-installing the jumpers and changing the settings of the DIP switches. The following illustration shows the location of the jumper blocks and the DIP Switches. Video Memory Video Feature Analog Video─┐ Upgrade│Sockets Connector│ Connector │ ┌────────┼────────────────────────────┐ │ ┌────────────────┐ │ │ ┌──────┼────┐ ┌────┐ │ ╔╦╦╦╦╦╦╦╦╦╦╦╗ │ │ │ │ └──────┼────┘ └────┘ └─╩╩╩╩╩╩╩╩╩╩╩╩╩─┘ │ │ │ ┌──────┼────┐ ┌──╫┐ │ │ └──────┼────┘ ┌────────────────┐ │ ║│ │ │ ┌──────┼────┐ │ │ │ ║│─┘ │ └──────┼────┘ │ │ ┌───────┐ └──╫┘ │ ┌──────┼────┐ │ │ │ │ │ │ └──────┴────┘ │ │ │ │ ┌╫┐ │ ┌┬─────┐ │ │ │ │ │║│ │ └┼─────┘┌─┐ └────────────────┘ └───────┘ │║│─┐ │ ┌┼─────┐└┬┘ └╫┘ │ │ └┼─────┘ │ ┌──────────────────┐ │ │ │ ┌┼─────┐ │ │ │ │ │ │ └┼─────┘ │ ┌────┐ ┌──┌─┐ │ │ │ │ │ ┌┼─────┐ │ └────┘ │ └─┘ │ │ │ │ │ └┼─────┘ │ │ └──────────────────┘ │ │ │ ┌┘ │ │ ┌───┐ ┌───┐ ┌───┐ │ │ │ │ │ │ └───┘ └───┘ └───┘ │ │ │ │ │ │ │ │ └────┼───╦╦╦╦╦╪╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╪╦─╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦╦─┐ │ │ │ ╚╩╩╩╩╪╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╪╝ ╚╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╩╜ └─┘ │ Video │ │ │ Memory │ │ Dip Switches │ │ Video Memory (W1) Wait State (W2) Configuration Jumper Jumper JUMPER SETTINGS A jumper is a cover that contains metal contacts. A jumper is installed when placed over two jumper pins on a circuit board to connect or bypass a circuit. A jumper can also be parked or removed. Jumper W1 is the Video Memory Configuration jumper. It is installed at the factory to indicate that the adapter has 512KB of video memory. Remove the jumper if you upgrade the adapter to 1MB of video memory. Jumper W2 is the Wait State jumper. It is installed at the factory to generate zero wait states and achieve maximum performance. Normally, you do not need to change this setting. NOTE: If you experience screen data loss, you might need to remove Jumper W2. Some computers do not support zero wait states. Jumper settings and their functions are listed in the following table. JUMPER SETTING FUNCTION W1 Installed* 512KB of video memory installed. Not Installed 1024KB of video memory installed. W2 Installed* Generate zero wait state for high performance. Not Installed Do not generate zero wait state. * Indicates factory setting. DIP SWITCH SETTINGS Five DIP switches are located below the video connector on the adapter, where they are easily accessible from the rear of the computer when the adapter is installed. A switch is off when in the left position, on when in the right position. CAUTION: Incorrect settings can cause a computer malfunction or a decrease in performance. Some switches are sensed only when you turn on the computer, so always turn off the computer before changing switch settings. To change a switch setting, use a pencil or other pointed instrument to push the switch to the left or right. The switch will snap into position. DIP switch settings and their functions are listed in the following tables. SWITCHES 1 AND 2 (MAXIMUM RESOLUTION 800 X 600) SWITCH 1 SWITCH 2 MAXIMUM MONITOR FREQUENCY OFF* OFF* 56 Hz ON OFF 72 Hz OFF ON 60 Hz ON ON 56 Hz (Same as OFF,OFF) * Indicates factory setting SWITCHES 3 AND 4 (MAXIMUM RESOLUTION 1024 X 768) SWITCH 3 SWITCH 4 MAXIMUM MONITOR FREQUENCY OFF* OFF* Interlaced ON OFF 70 Hz OFF ON 60 Hz ON ON Interlaced (same as OFF,OFF) * Indicates factory setting SWITCH 5 (TIMING FOR STANDARD MODES, 0 TO 13) OFF* 31.5 KHz horizontal scan rate ON 40 KHz horizontal scan rate * Indicates factory setting SERIAL PORT PROGRAMMING COM A (Serial Port A) Port Select Port Address Interrupts COM1 3F8-3FF IRQ4 COM3 3E8-3EF IRQ4 or IRQ11 COM B (Serial Port B) Port Select Port Address Interrupts COM2 2F8-2FF IRQ3 COM4 2E8-2EF IRQ3 or IRQ10 (jjs/tmc-05/25/95)