Digital VT320 Component List

I have the PCB from a Digital Model VT320-C3, made in Hong Kong. It is serial number HK83981214, dated 22 September 1988. It finally blew up in October 1997. I have not investigated which components are blown.

The most “interesting” components (those with serial numbers) are shown below. If my descriptions state the obvious, that is because I’m a software engineer, so I’m learning here! I have highlighted the major components in a photograph of the PCB. Many of these components are now obsolete but have pin-compatible replacements.

Siemens SAB8031A-16-P

ROMless version of the 8051 microcontroller, running at 16 MHz.

Motorola MC2681P

Dual Universal Asynchronous Receiver/Transmitter (DUART), 40-pin package. It appears that this drives the comms ports and the printer port. My model of the terminal has two comms ports, one DEC-423 with a DEC MMJ connector, and a 25-pin RS-232C connector. The printer port is also a 423 port with a 6-pin DEC MMJ connector.

Toshiba TC53512AP

ROM, 512K bits = 64K bytes. 28-pin package. I have experience of blowing EPROMs on the STAG programmer at work, so I assumed that the pinouts on this would be the same as the 27512s I’m used to. I plugged it into the programmer, told the programmer that I had a 27512 and uploaded the contents into memory.

Toshiba TC5565APL-12, 2 off

Static RAM, 64K bit = 8K byte. I think "12" means 120ns access time, but I don’t know whether this is a minimum or maximum time. Knowing this is not important to my emulator anyway.

ST TDA1170N

Vertical deflection system IC. This has 12 pins and two large tabs, which I am told are to help dissipate heat.

UC 80343Q

20 pins. Unknown.

UC 80068Q

20 pins. Unknown.

Motorola SN74LS157NQST

16 pins. Quad 2-to-1 multiplexer. This enables four bits of data to be selected and output from two sources. I don’t know what it does in this particular application.

Microchip ER5911

8 pins. Serial EEPROM. 1K bits = 128 bytes.

Texas Inst. 749X 75146

8 pins. Unknown.

Signetics? 74LS373N

8-bit D-type latch. This has eight inputs and eight outputs. These can be either transparent (input = output) or "frozen" (output = state of input at the freezing moment). I don’t know what it does in this particular application.

Thanks to Jerzy Sopicki for filling in some of the gaps here. Motorola Semiconductors had datasheets for some of these components (the 74 Series ones). Signetics’ web site was completely useless, with not even a search facility.