Siemens SIMATIC S7-200 System Manual page 352

S7-200 Programmable Controller System Manual
USS_RPM_x Instruction
There are three read instructions for the USS protocol:
USS_RPM_W (port 0) or USS_RPM_W_P1 (port 1)
-
instruction reads an unsigned word parameter.
USS_RPM_D (port 0) or USS_RPM_D_P1 (port 1)
-
instruction reads an unsigned double word parameter.
USS_RPM_R (port 0) or USS_RPM_R_P1 (port 1)
-
instruction reads a floating-point parameter.
Only one read (USS_RPM_x) or write (USS_WPM_x)
instruction can be active at a time.
The USS_RPM_x transactions complete when the
MicroMaster drive acknowledges receipt of the command,
or when an error condition is posted. The logic scan
continues to execute while this process awaits a response.
The EN bit must be on to enable transmission of a request,
and should remain on until the Done bit is set, signaling
completion of the process. For example, a USS_RPM_x
request is transmitted to the MicroMaster drive on each
scan when XMT_REQ input is on. Therefore, the XMT_REQ
input should be pulsed on through an edge detection
element which causes one request to be transmitted for
each positive transition of the EN input.
The Drive input is the address of the MicroMaster drive to
which the USS_RPM_x command is to be sent. Valid
addresses of individual drives are 0 to 31.
Param is the parameter number. Index is the index value of the parameter that is to be read. Value
is the parameter value returned. The address of a 16-byte buffer must be supplied to the DB_Ptr
input. This buffer is used by the USS_RPM_x instruction to store the results of the command
issued to the MicroMaster drive.
When the USS_RPM_x instruction completes, the Done output is turned on and the Error output
byte and the Value output contain the results of executing the instruction. Table 11-6 defines the
error conditions that could result from executing the instruction. The Error and Value outputs are
not valid until the Done output turns on.
Table 11-4 Valid Operands for the USS_RPM_x
Inputs/Outputs
XMT_REQ
Drive
Param, Index
DB_Ptr
Value
Done
Error
338
Data Type Operands
BOOL I, Q, M, S, SM, T, C, V, L, Power Flow conditioned by a rising edge
detection element
BYTE VB, IB, QB, MB, SB, SMB, LB, AC, *VD, *AC, *LD, Constant
WORD VW, IW, QW, MW, SW, SMW, LW, T, C, AC, AIW, *VD, *AC, *LD,
Constant
DWORD &VB
WORD VW, IW, QW, MW, SW, SMW, LW, T, C, AC, AQW, *VD, *AC, *LD
DWORD, REAL VD, ID, QD, MD, SD, SMD, LD, *VD, *AC, *LD
BOOL I, Q, M, S, SM, T, C, V, L
BYTE VB, IB, QB, MB, SB, SMB, LB, AC. *VD, *AC, *LD