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OUTPUT ENABLE CONNECTION
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Pin 24 is the output enable active low input used to control the logical state of the data lines. When this pin is HIGH, the
data lines are in the high impedance condition and no data is present on these pins. When the output enable input it LOW,
the data lines are active and output the addressed data, This line is connected to the data strobe output of the
microcontroller to ensure correct operation/timings.
CHIP ENABLE CONNECTION
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Pin 22 is the chip enable active low input used to select the device. Normally, this input is low to enable the device.
However, the device can be placed in a standby state when accessing a future SRAM in position I003. The MMU3 line
from the microcontroller is used to select either the SRAM or the MTP. When no SRAM is fitted, the chip enable pin is
always low.
MISCELLANEOUS
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Pin 1 (VPP) is the programming voltage input pin (+12.75V needed) used to re-program the device when placed in a
special programmer. This pin is always tied to the +5V standby supply, to ensure that the device can never be re-
programmed inside the television chassis.
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Pin 30 is not used in this device. However, it is still connected to the MMU1 line from the microcontroller for use with
larger size MTP's/EPROM's. This line can be used to access a further 128Kbytes if such a device was fitted.
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Pin 31 is the active-low programming enable pin that is used to re-program and erase the device. This pin is always
connected to the +5V standby supply to ensure that no inadvertent writes/erases are performed on the device.
SRAM (I003)
INTRODUCTION
On future chassis, the position I003 will be used to hold an SRAM for teletext page storage and memory storage. A 128Kbyte device
will most likely be situated here to allow 100 teletext pages to be acquired and stored for immediate fast access to them. The SRAM
is connected to the microcontroller's address and data lines, which are shared with the EPROM/MTP in position I002.
DESCRIPTION
SUPPLY/GROUND CONNECTIONS
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Pins 32 and 16 are the +5V supply and ground connections respectively. This device always has +5V connected to it,
even when the TV is in the standby state.
ADDRESS LINE CONNECTIONS
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Pins 2 to 12, 23, 31 and 25 to 28 are the address lines needed to access the 128Kbyte of data by the microcontroller.
DATA LINE CONNECTIONS
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Pins 13 to 15 and 17 to 21 are the 8-bit data lines needed to receive/transmit a byte of data at a time to/from the
microcontroller.
CHIP ENABLE CONNECTIONS
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Pins 22 and 30 are 2 chip enable inputs that need to be LOW and HIGH respectively for the 128Kbyte device to operate.
If either pin 22 is HIGH or pin 30 is LOW, then the device enters a standby state whereby its power consumption is
dramatically reduced (10uW). The MMU3 output pin from the microcontroller (pin 2) is used to select the SRAM when it is
HIGH. If this pin is low, then the MTP/EPROM in position I002 is selected instead.
WRITE ENABLE CONNECTIONS
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Pin 29 is the active-low write enable input used to enable data to be stored inside the device. This pin is connected to the
read/write line of the microcontroller for synchronisation purposes.
74HC04 HEX INVERTER (I004)
INTRODUCTION
The 14-pin IC in position I004 is a high speed CMOS hex inverter used to invert digital signals. The package consists of 6 inverters,
but only 4 are used in this application.
DESCRIPTION
SUPPLY/GROUND CONNECTIONS
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Pins 14 and 7 are the +5V and 0V supply connections respectively. This device always has +5V supplied to it, even when
the TV is in the standby state. Capacitor C023 is connected across the supply terminal for de-coupling.
CHIP ENABLE CONNECTION
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Pin 1 is connected to the MMU3 output from the microcontroller and is used to select either the MTP or the SRAM. This
signal is inverted and output from pin 2 that is then connected to the active low chip enable input (pin 22) of the SRAM. In
this way, only one chip enable line from the microcontroller needs to be used to enable the SRAM.
All manuals and user guides at all-guides.com
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