Tektronix 2715 Memory

Theory of Operation

2715 Spectrum Analyzer Service Manual 3-65

Reading from a module begins with the module requesting service through its

activelow request signal (FPREQ-- for the front panel, ...).This signal goes into

a priority encoder (U780)on the Power Supply Secondaries, then pulls the

Microprocessor boardInterrupt Handler, IRQ1, high. The outputs of the priority

encoder are then used to acknowledgethe request for service that activates the

output buffers on the module requesting service.At the same time, the outputs of

the priority encoder,ADI0 through ADI2, are fed into the I/O Subsystem status

address of the module requesting serviceis determined from the ADI0 through

ADI2 lines. Now the process of reading in the data from the module requesting

service can begin.

The lowest bit of the I/O Subsystem status register contains the data from the

module to be read. After each CLKI--signal , the status register is read and the

data is linked together in a s eries until all data has been received. The C LKI--

signal is generated the same way as the C LKO-- sign al described earlier.

The memory on the Microprocessorboard consists of two sections, 128 kilobytes

(16 ×8 kilobytes) of Random Access Memory (RAM), and up to 524 k ilobytes

(64 ×8 kilobytes) of Read Only Memory (ROM). The RAM is used forC PU

processing and data space, wh ile the ROM contains all of the system firmware.

Access to the RAM, for eith er reading or writing, consists of sending out the

address for the byte to be accessed. This addres s is decoded by U515, and the

appropriate enableline pulled low to select the memory device that is to be

accessed.

Access to the ROM (read only) is performed in th es ame way as the RAM.

Jumpers (and wires for a more permanentmethod) are provided on the Micropro-

cessor board for selectingthe size of EPROM and RAM memory chips used.

Table3 --16 shows the configuration of jumpers/wires for various size memory

ICs.

Table3 -16: Configuration of Jumpers/Wires for

VariousMemor y ICSizes

MemorySize Jumpers/Wires to Install

27256 W525A W518B

27512 W525A W518A W522

27010 W525A W518A

27020 W525B W518A

43256 W526A

4364 W526B

Memory