HP 3336A Operating Manual page 48

S
Model 3336A/B/C
These front panel controls or operations are NOT available to the
HP-IB programmer:
—Afx2 —display BUS ADDRESS
—Af-—2 —all controls in the Modify Group
—MKR-CF —CLEAR display
These HP-IB operations are NOT available from the front panel:
—Data Transfer Mode Selection
—Service Request Masking
—lInterrogration of Programming Errors
3-154. Data Transfer Mode Selection. The -hp- 3336 accepts Data Messages in one of two
Data Transfer Modes.
a. Data Transfer Mode |. The -hp- 3336 is in Data Transfer Mode | at turn-on and while
in this mode, each Instrument Programming Code is processed when received. That is, the
instrument immediately performs the instruction. The -hp- 3336 can NOT receive another
character until the instrument has completely performed the previous instruction. The time
required to transfer data has been extended by the time -hp- 3336 takes to perform the in-
struction. The advantage of Mode 1 is that it is less complicated to use but as your system
sophistication increases, the advantage of faster programming time makes Data Transfer
Mode 2 important.
b. Data Transfer Mode 2. The -hp- 3336 accepts and stores a string of Program Instruc-
tion Codes in an internal buffer when it is in Data Transfer Mode 2. These codes are NOT
processed until the buffer is full (48 characters) or the EOS (End of String) character is
received. The advantage of Data Transfer Mode 2 is that after a string of instructions is sent
to the -hp- 3336, at the fastest rate the instrument can accept them (150-200 usec per
character), communication can take place between other devices on the bus. A ''Busy'' flag,
encoded into bit 7 of the Status Byte, indicates when the instrument is ''Busy'' processing a
string of instructions. The instrument can NOT accept Data Messages during the time it is
"*Busy''. If a string longer than 48 characters is sent, the instrument will '"'hold up'' the bus
until the first 48 characters are processed and the remaining characters are accepted.
Therefore, to realize the maximum effectiveness, a program string longer than 48 characters
should be divided and an EOS character sent after (or at a convenient place before) the 48th
character. Data Transfer Mode 2 must be remotely programmed. The instrument will re-
main in Mode 2 until Mode 1 is programmed or the POWER switch is set to STBY.
Operation
3-27