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~SO_F_T_W_A_R_E_U_S_A_G_E_A_N_D_EX_A_M_P_L_E_S_--llrd!iH1'\
This section of the manual will provide supplemental information about the operation of the modem,
electronic disc, and bar code software, and examples of the use of the software.
OVERVIEW OF MODEM OPERATION
There are two types of modem commands provided by the HP 827l8A.
High -level modem commands
are
BASIC keywords that add to the set of commands you can execute from the keyboard or put in BASIC
programs. Examples of high-level commands are
t'1ODEt'1
Ot·~
(turn on the modem),
t'1ODOUT
(send a
string to the modem),
and
CAF.:F.: I
EF::?
(check if there is a carrier).
Low-level modem commands
are
commands that tell the modem to perform a specific action. Examples of low-level commands are D
(dial
a phone number),
F
(set data format or parity),
and 0
(enter ORIGINATE mode).
The HP-7 5 communicates
with the modem primarily with two high-level modem commands:
t'10DOUT
and
t'10D
HU:.
These
BASIC keywords are the real workhorses of the HP-75/modem system.
t'10DOUT
sends data and
low-level modem commands from the HP-75 to the modem.
t'1OD I
t·U::
reads the contents of the modem
receive buffer and returns that data to the HP-7S. In addition, six other high-level modem commands
identify certain modem status conditions, such as parity and framing errors, carrier detected, etc. Below is
a block diagram of the HP-7S/modem system.
HP 82718A MODEM
I
MODEM COMMANDS
I
MODOUT
t
TO PHONE LINE
' I
TRANSMIT BUFFER
I
I
HP-75
MODIN$
I
I
FROM PHONE LINE
I
RECEIVE BUFFER
i
I
MODEM RESPONSES
1
AVAIL?, CARRIER?, FRAME?,
I
I
I
STATUS
HOOK?, PARITY?, READY?
When
t'10DOUl
sends a string from the HP-7S to the modem, it places the string in the 8-byte modem
transmit buffer. The modem then examines the transmit buffer to see what action it should take. If the
15
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