External Connections
54 – Installation
VL-486-4 Reference Manual
J6 – DMA C
ONTROL
S
IGNALS
C
ONNECTOR
A 10-pin header connector, J6, provides external access to the on-board DMA channels.
Table 30: DMA Control Signals Connector Pinout.
J6
Pin
Signal
Name
Function
1
Ground
Ground
2
FPRQ*
Front plane DRQ
3
Ground
Ground
4
FPAK*
Front plane DAK
5
Ground
Ground
6
XIWR*
Front plane WR
7
Ground
Ground
8
XIRD*
Front plane RD
9
Ground
Ground
10
TC*
Terminal Count
FPRQ* — Front Plane DMA Request.
This TTL input signal is used to request DMA
transfer cycles. If jumper V3 is inserted, a low level applied to the FPRQ* pin will initiate a 16-
bit transfer using DMA channel 7. If jumper V3 is removed, an 8-bit transfer using DMA
channel 3 is performed. FPRQ* should be held low until FPAK* makes a low-to-high transition.
FPAK* — Front Plane DMA Acknowledge.
A low level on this TTL output signal
indicates that the DMA controller has accepted a DMA request on the FPRQ* input signal and is
preparing to transfer data. When FPAK* returns high, FPRQ* should be returned to the high
state.
FPWR* — Front Plane DMA Write.
A low level on this TTL output signal tells external
equipment to latch data from the STD Bus. The DMA controller provides this data from a
previous memory fetch.
FPRD* — Front Plane DMA Read.
A low level on this TTL output signal tells external
equipment to drive data onto the STD Bus. The DMA controller receives the data and saves it in
memory.
TC* — Terminal Count.
A low level on this TTL output signal indicates that the count
register has decremented from 0000h to FFFFh, signaling completion of a block of DMA
transfers.